Synthesis and characterization of platinum(II)-Bis(boryl) catalyst precursors for diboration of alkynes and diynes: Molecular structures of cis-[(PPh3)2Pt(B-4-Butcat)2], cis-[(PPh3)2Pt(Bcat)2], cis-[(dppe)Pt(Bcat)2], cis-[(dppb)Pt(Bcat)2]

Article abstract of DOI:10.1021/om950918c

The reactions of the B-B-bonded compounds B₂(cat)₂ (cat = 1,2-O₂C₆H₄) (1a), B₂(4-Bu^t-cat)₂ (1b), and B₂(OCMe₂CMe₂O)₂ (1c) with the Pt(0)-bis(phosphine) complex [(PPh₃)₂Pt(η-C₂H₄)] (4) via oxidative addition of the B-B bond yield cis-bis(boryl) Pt(II) complexes. The molecular structures of cis-[(PPh₃)₂Pt(Bcat)₂]·C ₆D₆ (3a) and cis-[(PPh₃)₂Pt(B-4-Bu^tcat)₂] (3b) were determined by single-crystal X-ray diffraction. Reaction of 3a with 1 equiv of the bidentate phosphine dppe (Ph₂PCH₂CH₂PPh₂) or dppb (Ph₂P(CH₂)₄PPh₂) proceeds smoothly in toluene to give cis-[(dppe)Pt(Bcat)₂] (5a) and cis-[(dppb)Pt(Bcat)₂] (5b), respectively, which have also been characterized by X-ray diffraction. Compounds 3a,b and 4 are highly active catalyst precursors for the diboration of alkynes and 1,3-diynes. X-ray crystal structures of (E)-(4-MeOC₆H₄)C(Bcat)=CH(Bcat) (10c), (Z)-(C₆H₅)C(Bcat)=C(C₆H₅)(Bcat) (10e), and (Z,Z)-(4-MeOC₆H₄)C(Bcat)=C(Bcat)C(Bcat)=C(4-MeOC ₆H₄)(Bcat) (14a) confirm the cis stereochemistry of the boron substituents in three representative cases, namely, products of the catalyzed diboration of the terminal alkyne 4-MeOC₆H₄C=CH, the internal alkyne PhC=CPh, and the tetraboration of the diyne 4,4′-MeOC₆H₄C=CC=CC₆H₄OMe. The presence of the C=CSiMe₃ moiety in catalytic reactions gives rise to additional products other than those derived from the diboration of the alkyne group. Metathetical reactions involving the diboron reagent and products derived from C-Si bond cleavage give rise to novel tris(boronate esters) as a result of the subsequent diboration of the C=CB(OR₂) moieties formed by this competing process. The absence of catalytic activity using compound 5a, the extremely low activity of 5b, and the strong decrease in activity of 3b in the presence of added PPh₃ suggests that phosphine dissociation is a critical step in the catalytic pathway.

Full text of DOI:10.1021/om950918c

Organometallics 1996, 15, 5137-5154
5137
Syn th esis a n d Ch a r a cter iza tion of
P la tin u m (II)-Bis(bor yl) Ca ta lyst P r ecu r sor s for
Dibor a tion of Alk yn es a n d Diyn es: Molecu la r Str u ctu r es
of cis-[(P P h 3)2P t(B-4-Bu tca t)2], cis-[(P P h 3)2P t(Bca t)2],
cis-[(d p p e)P t(Bca t)2], cis-[(d p p b)P t(Bca t)2],
(E)-(4-MeOC6H4)C(Bca t)dCH(Bca t),
(Z)-(C6H5)C(Bca t)dC(C6H5)(Bca t), a n d
(Z,Z)-(4-MeOC6H4)C(Bca t)dC(Bca t)C(Bca t)dC(4-MeOC6H4)(Bca t)
(ca t ) 1,2-O2C6H4; d p p e ) P h 2P CH2CH2P P h 2; d p p b )
P h 2P (CH2)4P P h 2)
Gerry Lesley, Paul Nguyen, Nicholas J . Taylor, and Todd B. Marder*
Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
Andrew J . Scott, William Clegg, and Nicholas C. Norman*,†
Department of Chemistry, University of Newcastle-upon-Tyne,
Newcastle-upon-Tyne NE1 7RU, England
Received November 28, 1995X
The reactions of the BsB-bonded compounds B2(cat)2 (cat ) 1,2-O2C6H4) (1a ), B2(4-But-
cat)2 (1b), and B2(OCMe2CMe2O)2 (1c) with the Pt(0)-bis(phosphine) complex [(PPh3)2Pt(η-
C2H4)] (4) via oxidative addition of the BsB bond yield cis-bis(boryl) Pt(II) complexes. The
molecular structures of cis-[(PPh3)2Pt(Bcat)2]‚C6D6 (3a ) and cis-[(PPh3)2Pt(B-4-Butcat)2] (3b)
were determined by single-crystal X-ray diffraction. Reaction of 3a with 1 equiv of the
bidentate phosphine dppe (Ph2PCH2CH2PPh2) or dppb (Ph2P(CH2)4PPh2) proceeds smoothly
in toluene to give cis-[(dppe)Pt(Bcat)2] (5a ) and cis-[(dppb)Pt(Bcat)2] (5b), respectively, which
have also been characterized by X-ray diffraction. Compounds 3a ,b and 4 are highly active
catalyst precursors for the diboration of alkynes and 1,3-diynes. X-ray crystal structures of
(E)-(4-MeOC6H4)C(Bcat)dCH(Bcat) (10c), (Z)-(C6H5)C(Bcat)dC(C6H5)(Bcat) (10e), and (Z,Z)-
(4-MeOC6H4)C(Bcat)dC(Bcat)C(Bcat)dC(4-MeOC6H4)(Bcat) (14a ) confirm the cis stereo-
chemistry of the boron substituents in three representative cases, namely, products of the
catalyzed diboration of the terminal alkyne 4-MeOC6H4CtCH, the internal alkyne PhCtCPh,
and the tetraboration of the diyne 4,4′-MeOC6H4CtCCtCC6H4OMe. The presence of the
CtCSiMe3 moiety in catalytic reactions gives rise to additional products other than those
derived from the diboration of the alkyne group. Metathetical reactions involving the diboron
reagent and products derived from CsSi bond cleavage give rise to novel tris(boronate esters)
as a result of the subsequent diboration of the CtCB(OR2) moieties formed by this competing
process. The absence of catalytic activity using compound 5a , the extremely low activity of
5b, and the strong decrease in activity of 3b in the presence of added PPh3 suggests that
phosphine dissociation is a critical step in the catalytic pathway.
In tr od u ction
catalytic addition of B-B bonds to alkenes2 and alkynes3
have only just begun to appear. The diboron tetraha-
lides B2X4 (X ) F, Cl, Br) add readily across C-C
multiple bonds in the absence of a catalyst; however,
difficulties with the preparation and isolation of these
reagents present considerable drawbacks for routine
use.4 We have recently reported5 the oxidative addition
of B-B bonds in B2(OR)4 ((OR)2 ) cat ) 1,2-O2C6H4 (1a );
(OR)2 ) 4-Butcat ) 1,2-O2-4-ButC6H3 (1b)) compounds
While metal-catalyzed alkene hydroboration has re-
ceived much attention1 in recent years, studies of the
† Present address: University of Bristol, School of Chemistry, Bristol
BS8 1TS, England.
X Abstract published in Advance ACS Abstracts, J une 1, 1996.
(1) For leading references, see: (a) Ma¨nnig, D.; No¨th, H. Angew.
Chem., Int. Ed. Engl. 1985, 24, 878. (b) Burgess, K.; Ohlmeyer, M. J .
Chem. Rev. 1991, 91, 1179. (c) Evans, D.; Fu, G. C. J . Am. Chem. Soc.
1992, 114, 6679. (d) Gridnev, I. D.; Miyaura, N.; Suzuki, A. J . Org.
Chem. 1993, 58, 5351. (e) Brown, J .; Lloyd-J ones, G. C. J . Am. Chem.
Soc. 1994, 116, 866. (f) Matsumoto, Y.; Naito, M.; Uozumi, Y.; Hayashi,
T. J . Chem. Soc., Chem. Commun. 1993, 1468. (g) Hou, X.; Hong, D.;
Rong, G.; Guo, Y.; Dai, L. Tetrahedron Lett. 1993, 34, 8513. (h)
Westcott, S. A.; Blom, H. P.; Marder, T. B.; Baker, R. T. J . Am. Chem.
Soc. 1992, 114, 8863. (i) Burgess, K.; Van der Donk, W. A.; Westcott,
S. A.; Marder, T. B.; Baker, R. T.; Calabrese, J . C. J . Am. Chem. Soc.
1992, 114, 9350. (j) Harrison, K. N.; Marks, T. J . J . Am. Chem. Soc.
1992, 114, 9220. (k) Pereira, S.; Srebnik, M. Organometallics 1995,
14, 3127.
(2) Baker, R. T.; Nguyen, P.; Marder, T. B.; Westcott, S. A. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1336.
(3) (a) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J . Am.
Chem. Soc. 1993, 115, 11018. (b) Ishiyama, T.; Matsuda, N.; Murata,
M.; Ozawa, F.; Suzuki, A.; Miyaura, N. Organometallics 1996, 15, 713.
(4) (a) Morrison, J . A. Chem. Rev. 1991, 91, 35. (b) Massey, A. G.
Adv. Inorg. Chem. Radiochem. 1983, 26, 1.
(5) Nguyen, P.; Lesley, G.; Taylor, N. J .; Marder, T. B.; Pickett, N.
L.; Clegg, W.; Elsegood, M. R. J .; Norman, N. C. Inorg. Chem. 1994,
33, 4623.
S0276-7333(95)00918-6 CCC: $12.00 © 1996 American Chemical Society

5138 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
Sch em e 1
than two 2 bound phosphine ligands, (2) the presence
of additional phosphine might inhibit catalyst activity,
and (3) B2(cat)2 might show enhanced reactivity com-
pared with B2(pin)2.5 In this paper, we report the
synthesis and characterization of a series of cis-bis-
(phosphine)platinum(II) bis(boryl) complexes and their
activity as catalyst precursors for alkyne diboration
reactions.3 The effects of the nature and concentration
of phosphine ligands on the catalytic activity of the Pt
complexes will be discussed, as will the relative reactiv-
ity of the diboron reagents involved in these reactions.
to Rh(I) centers and have demonstrated catalyzed
addition2 of 1a to styrenes using both Rh and Au
catalyst precursors. We also reported6 that stoichio-
metric reactions of a Rh(III) bis(boryl) complex with
alkenes gave both the expected alkyl-1,2-bis(boronate
ester) diboration product as well as products derived
from alkene insertion into Rh-B bonds followed by
facile â-hydride elimination. Miyaura and Suzuki et al.
first reported3a NMR evidence that reactions of 10 equiv
of B2(pin)2 (pin ) OCMe2CMe2O; 1c) with [Pt(PPh3)4]
(2) gave the platinum bis(boryl) complex cis-[(PPh3)2-
Pt(Bpin)2] (3c) and that 2 is a catalyst precursor for the
addition of 1c to alkynes (24 h at 80 °C in DMF using
3 mol % of 2). Recently, the same authors have isolated
and fully characterized compound 3c from the reaction
of 2 with 20 equiv of B2(pin)2.3b While the present work
was in progress, Iverson and Smith also reported7a that
[(PPh3)2Pt(η-C2H4)] (4) reacts with B2(cat)2 with loss of
ethylene, yielding cis-[(PPh3)2Pt(Bcat)2] (3a ), and that
3a reacts stoichiometrically with 4-octyne in the pres-
ence of 1.5 mol equiv of B2(cat)2 to give the 1,2-vinyl-
bis(boronate ester) diboration product and 3a . The
metallacyclopentane [(PPh3)2Pt(CH2)4] also reacts with
2 mol equiv of B2(cat)2 (8 h, 95 °C), yielding 3a and
catB(CH2)4Bcat. These authors have recently described
the synthesis and characterization of compound 3c by
a different synthetic route requiring only stoichiometric
quantities of B2(pin)2.7b
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of cis-[(R3P )2P t-
(bor yl)2] Com p ou n d s. Isolated samples9 of [(PPh3)2-
Pt(η-C2H4)] (4) react rapidly with 1.1 mol equiv of
B2(cat)2 (1a ) in C6D6 or toluene at room temperature to
give cis-[(PPh3)2Pt(Bcat)2] (3a ) in excellent yield (88%,
based on the toluene solvate) and purity as a white
precipitate (Scheme 1). Likewise, 4 reacts rapidly with
1b to give cis-[(PPh3)2Pt(B-4-Butcat)2] (3b) in similar
yield and purity. The yield of 3a is greater than that
previously reported (75%)7a for the same reaction.
Analysis of the filtrate from the reaction mixture
indicates the presence of additional 3a together with
associated decomposition products (vide infra). This
indicates that the reaction is nearly quantitative but
that some solubility in toluene and slight decomposition
in solution account for the less than 100% yields of the
isolated precipitates. For compound 3b, the enhanced
solubility in toluene due to the presence of the tert-butyl
groups is the main source for a reduction of the overall
isolated yield of crystallized product from toluene. In
this case the filtrate indicates the presence of 3b with
negligible decomposition over a period of 24 h. The
enhanced stability of isolated 3b vs 3a is also observed
in CDCl3 solutions. The stoichiometric reaction (1:1.1)
of 4 with B2(pin)2 to form cis-[(PPh3)2Pt(Bpin)2] (3c) was
incomplete after stirring overnight in CDCl3 or C6D6,
and the products from this reaction could not be isolated
due to the presence of decomposition products arising
from 4 and 1c as discussed below. The formation of 3c
was enhanced when THF was added to the reaction
mixture in C6D6. The exact role of THF for this
enhancement or shift in the equilibrium is unknown.
As mentioned previously, two independent research
groups have recently described synthetic routes for the
isolation of 3c with yields ranging from 70%7b to 82%.3b
In conjunction with our studies of metal-polyboryl
complexes5,6,8 and B-B oxidative addition to Rh(I),5 Co-
(0),8b and Ir(I),8c we investigated reactions of the Pt(0)
complex 4 with diboron compounds 1a -c and also began
a study aimed at developing new diboration catalyst
precursors with enhanced activities. We reasoned that
(1) the active Pt catalyst was unlikely to possess more
(6) Baker, R. T.; Calabrese, J . C.; Westcott, S. A.; Nguyen, P.;
Marder, T. B. J . Am. Chem. Soc. 1993, 115, 4367.
(7) (a) Iverson, C. N.; Smith, M. R., III. J . Am. Chem. Soc. 1995,
117, 4403. (b) Iverson, C. N.; Smith, M. R., III. Organometallics, in
press.
(9) Camalli, M.; Caruso, F.; Chaloupka, S.; Leber, E. M.; Rimml,
H.; Venanzi, L. M. Helv. Chim. Acta 1990, 73, 2263. This paper
provides a convenient synthetic route to the isolation of several bis-
(phosphine)Pt(η-C2H4) complexes from the corresponding P2PtCl2
compounds. We have used the same synthetic route, with the exception
that THF was substituted for CH2Cl2 to prepare 4, [(dppe)Pt(η-C2H4)],
and [(dppb)Pt(η-C2H4)] as isolable solids. 31P{1H} NMR (81 MHz,
CDCl3): 4, δ 34.3 ppm (J Pt-P ) 3721 Hz); [(dppe)Pt(η-C2H4)], δ 54.4
ppm (J Pt-P ) 3303 Hz); [(dppb)Pt(η-C2H4)], δ 25.5 (J Pt-P ) 3524 Hz).
The in situ preparation of [(dppe)Pt(η-C2H4)] has been described pre-
viously: Head, R. A. J . Chem. Soc., Dalton Trans. 1982, 1637; Inorg.
Synth. 1990, 28, 132 (δP 54.5 ppm; J Pt-P ) 3300 Hz).
(8) (a) Nguyen, P.; Blom, H. P.; Westcott, S. A.; Taylor, N. J .; Marder,
T. B. J . Am. Chem. Soc. 1993, 115, 9329. (b) Dai, C.; Stringer, G.;
Corrigan, J . F.; Taylor, N. J .; Marder, T. B.; Norman, N. C. J .
Organomet. Chem. 1996, 513, 273. (c) Dai, C.; Stringer, G.; Marder,
T. B.; Baker, R. T.; Scott, A. J .; Clegg, W.; Norman, N. C. Can. J . Chem.,
in press. (d) For additional examples of metal bis(boryl) complexes
see: Hartwig, J . F.; He, X. Organometallics 1996, 15, 400. (e) Cp2W(B-
4-Butcat)2 has recently been structurally characterized: Hartwig, J .
F.; He, X. Angew. Chem., Int. Ed. Engl. 1996, 35, 315.

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5139
Sch em e 2
the resonances, which is apparently due to strong
coupling with the quadrupolar boron nuclei. The previ-
ously reported7a chemical shift for 3a is slightly different
from values in this work, presumably due to solvent
effects.
The 1H NMR results are also consistent with previous
values reported for 3a . The aromatic region exhibits
broad multiplets for the aryl rings in the phosphine
ligand and for those associated with the 1,2-disubsti-
tuted aryl ring of the boryl ligands. In the 1H NMR
spectrum of 3b there is coincidental overlap of two of
the aromatic hydrogen atom resonances (δ 6.68 ppm,
both with J H-H values of 1.1 Hz) associated with the
boryl ligand.
The 13C NMR spectra of compounds 3a and 5a ,b
exhibit similar resonances due to the Bcat ligands. The
ipso carbon atoms resonate farthest downfield at ca. 150
3
ppm, and all have J Pt-C values of ca. 34 Hz (the
satellites were too weak to observe for compound 5a ).
The carbon atoms in the 3- and 6-positions resonate
farthest upfield at ca. 110 ppm, while the resonances
due to the carbon atoms in the 4- and 5-positions are
slightly downfield of this at ca. 120 ppm. In the
spectrum of compound 3b, the carbon atoms in the 1-
and 2-positions are inequivalent due to the tert-butyl
substitution on the ring, and separate resonances each
Further reaction of 3a with 1.0 mol equiv of the
bidentate phosphines dppe (1,2-bis(diphenylphosphino)-
ethane) and dppb (1,4-bis(diphenylphosphino)butane) in
toluene at room temperature results in fine white
precipitates of cis-[(dppe)Pt(Bcat)2] (5a ) and cis-[(dppb)-
Pt(Bcat)2] (5b), respectively (Scheme 2). Analysis of the
31P{1H} NMR spectra of all fractions indicates clean
reactions resulting in quantitative yields. As with
previous results, however, some solubility of the prod-
ucts in toluene reduced isolated yields of 5a ,b to ca. 76-
77%. Solutions of 5a (CDCl3 or C6D6/THF) and 5b
(CDCl3) were stable over a period of 24 h. Alternatively,
compounds 5a ,b may also be prepared by direct oxida-
tive addition of 1a to the corresponding [P2Pt(η-C2H4)]
complexes;9 however, these reactions were not as clean
as those described above due to impurities present from
the synthesis of the Pt ethylene complexes.
3
with J Pt-C values of 35 Hz are observed. The substitu-
tion in the 4-position also causes a downfield shift of
the resonance due to the carbon atom at this position
in the ring (143.2 ppm). The resonances for the ipso
carbon of the P(C6H5)3 ligands could not be character-
ized completely in all of the 13C NMR spectra, due to
partial overlap with the multiplets arising from the
carbon atoms in the ortho position on the phenyl rings.
As a result of this overlap, the resonances reported in
the Experimental Section for compounds 3a and 5a are
therefore not expected to be singlets but rather doublets
with a slightly upfield chemical shift relative to that
reported. In the spectrum of 3b, coupling to Pt (2J Pt-C
) 20 Hz) and P (1J P-C ) 44 Hz) was observed for the
ipso carbon. In the spectrum of 5a only the coupling to
P (1J P-C ) 47 Hz) was observed.
Complexes 3a -c and 5a ,b were characterized by
1
melting point, H, 11B, 13C, and 31P NMR spectroscopy,
Molecu la r St r u ct u r e of cis-[(R 3P )2P t (b or yl)2]
Com p ou n d s. In all cases, the structures of the Pt
compounds display a cis-square-planar arrangement of
the two phosphine and boryl ligands. The B(1)-B(2)
distances (2.552 Å (3a ), 2.554 Å (3b), 2.667 Å (5a ), 2.514
Å (5b)) are large and indicate the absence of an
interaction between the B atoms (B(1)-B(2) ) 1.678(3)
Å for 1a 5). In the structure of cis-[(PPh3)2Pt(Bcat)2]
(3a ; Figure 1) the Pt-B distances average 2.049(6) Å,
which is typical of third-row late-metal M-B bond
lengths.7a,8ac,11 The B(1)-Pt(1)-B(2) angle is consider-
ably smaller than 90°, being 77.1(2)°, whereas the P(1)-
Pt(1)-P(2) angle is 107.14(4)°. The conformations about
the Pt-B bonds are such that the Bcat groups form
interplanar angles of 71.3° (mean plane B(1), O(1), O(2),
C(1)-C(6)) and 82.7° (mean plane B(2), O(3), O(4),
C(11)-C(16)) with respect to the mean plane defined
by Pt, B(1), B(2), P(1), P(2).
and elemental analysis (except for 3c) and for 3a ,b
(Figures 1 and 2) and 5a ,b (Figures 3 and 4) by single-
crystal X-ray diffraction. Each sample underwent a
noticeable color change from white to yellow to orange
prior to melting, and the temperature at which this
decomposition became apparent is noted in parentheses
in the Experimental Section.
The 31P{1H} NMR spectra exhibit broad resonances
with |J Pt-P| values consistent with the cis coordination
of the boryl ligands10 (δP 28.7, J Pt-P ) 1639 Hz, 3a ; δP
29.0, J Pt-P ) 1621 Hz, 3b; δP 28.5, J Pt-P ) 1504 Hz, 3c)
and agree well with previously reported values for 3a
(C6D6, δP ) 30.19, J Pt-P ) 1608 Hz)7a and 3c (toluene,
δP 28.65, J Pt-P ) 1517 Hz);3a however, discrepancies in
the 11B{1H} NMR spectra (δB 21.5,3a δB 46.3,3b ca. 50
ppm (this work)) arise. We have prepared an authentic
sample of B2(pin)3 (7) which is consistent with the 11B
resonance reported in the initial study by Suzuki et al.,3a
as described in further detail in the section dealing with
the decomposition of catalysts below. Slight deviations
in |J Pt-P| values are expected due to the broadness of
(11) (a) Knorr, J . R.; Merola, J . S. Organometallics 1990, 9, 3008.
(b) Baker, R. T.; Ovenall, D. W.; Calabrese, J . C.; Westcott, S. A.;
Taylor, N. J .; Williams, I. D.; Marder, T. B. J . Am. Chem. Soc. 1990,
112, 9399. (c) Lu, Z.; J un, C.-H.; de Gala, S. R.; Sigalas, M.; Eisenstein,
O.; Crabtree, R. H. J . Chem. Soc., Chem. Commun. 1993, 1877. (d)
Westcott, S. A.; Marder, T. B.; Baker, R. T.; Calabrese, J . C. Can. J .
Chem. 1993, 71, 930.
(10) The authors in refs 3a and 7a have discussed this issue in terms
of related Pt bis(silyl) complexes and the trans effect of the Bcat group,
respectively.

5140 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
F igu r e 3. Molecular structure of cis-[(Ph2PCH2CH2PPh2)-
Pt(B(1,2-O2C6H4))2] (5a ), with 50% probability ellipsoids.
F igu r e 1. Molecular structure of cis-[(PPh3)2Pt(B(1,2-
O2C6H4))2] (3a ), with 50% probability ellipsoids.
F igu r e 4. Molecular structure of cis-[(Ph2P(CH2)4PPh2)-
Pt(B(1,2-O2C6H4))2] (5b), with 50% probability ellipsoids.
and the structure is therefore more similar to 3a ,b than
to 5a . The conformations about the Pt-B bonds are also
more similar to 3a ,b than to 5a in that the Bcat groups
form interplanar angles of 81.4° (mean planes B(1), O(1),
O(2), C(1)-C(6) and B(1a), O(1a), O(2a), C(1a)-C(6a))
with respect to the mean plane defined by Pt, B(1), B(2),
P(1), P(2).
F igu r e 2. Molecular structure of cis-[(PPh3)2Pt(B(1,2-O2-
4-ButC6H4))2] (3b), with 50% probability ellipsoids.
The structure of cis-[(PPh3)2Pt(B(4-Butcat))2] (3b;
Figure 2) is very similar to that of 3a . The Pt-B
distances average 2.046(13) Å, and the B(1)-Pt(1)-B(2)
angle is also considerably smaller than 90°, being
77.2(4)°, while the P(1)-Pt(1)-P(2) angle is 104.37(10)°.
The B(4-Butcat) groups form interplanar angles of 75.9°
(mean plane B(1), O(1), O(2), C(1)-C(6)) and 86.7°
(mean plane B(2), O(3), O(4), C(11)-C(16)) with respect
to the mean plane defined by Pt, B(1), B(2), P(1), P(2).
In the structure of cis-[(dppe)Pt(Bcat)2] (5a ; Figure
3), the Pt-B distances average 2.053(8) Å, similar to
3a ,b, but the B(1)-Pt(1)-B(2) angle is opened to
81.0(3)°, concomitant with the P(1)-Pt(1)-P(2) angle
being reduced to 85.36(6)° due to the presence of the
five-membered chelate ring. The conformations about
the Pt-B bonds are also rather different from those
observed for 3a ,b such that the Bcat groups form
interplanar angles of 55.1° (mean plane B(1), O(1), O(2),
C(1)-C(6)) and 88.8° (mean plane B(2), O(3), O(4),
C(11)-C(16)) with respect to the mean plane defined
by Pt, B(1), B(2), P(1), P(2).
The structure of 3a has been recently reported;7a
however, the results in this work provide significantly
more precise structural parameters (e.g. previous values
were Pt-B(1) ) 2.08(2) Å, Pt-B(2) ) 2.07(2) Å). In
addition, while this paper was in preparation, Miyaura
et al.3b reported the structural characterization of
compound 3c. It is interesting that the B(1)-Pt-B(2)
angle is reduced even further in this structure to a value
of 75.3(3)°. The Pt-B(1) and Pt-B(2) bond lengths
(2.076(6) and 2.078(6) Å, respectively) are also slightly
longer than those observed in this study, indicating a
slight weakening of the metal-boryl bond with respect
to the related catecholate derivatives.
Ca ta lytic Rea ction s. The catalytic activity of 3b
and 4 for the addition of B-B bonds to internal and
terminal alkynes (Scheme 3) and 1,3-diynes (Scheme 4)
was examined using 1a ,c and 1-octyne (8a ), C6H5CtCH
(8b), 4-MeOC6H4CtCH (8c), 4-NCC6H4CtCH (8d ),
C6H5CtCC6H5 (8e), 4-MeC6H4CtCC6H4-4-Me (8f),
4-MeOC6H4CtCC6H4-4-OMe (8g), Me3SiCtCSiMe3 (8h ),
4-MeOC6H4CtCCtCC6H4-4-OMe (9a ), and Me3SiCtC-
CtCSiMe3 (9b). Typical reaction conditions employed
1.9 × 10-4 mol of alkyne, 1.9 × 10-4 mol of diboron
In the structure of cis-[(dppb)Pt(Bcat)2] (5b; Figure
4), the Pt-B distances are both 2.031(8) Å, the B(1)-
Pt(1)-B(2) angle is reduced to 76.5(4)°, concomitant
with the P(1)-Pt(1)-P(2) angle opening to 100.72(9)°,

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5141
logues R1C(Bcat)dC(Bcat)R2 (10a -g) and in some cases
have been isolated previously by Kugelrohr distillation.3
In this work, the products in the crude reaction mixtures
were analyzed directly by NMR spectroscopy (1H, 13C,
and 11B) and GC/MS, and both techniques were used to
determine the degree of completion of the reactions.
Unless otherwise stated, the reactions proceeded to
100% completion. Initial attempts to isolate the prod-
ucts from the scaled-up reaction (ca. 2 mmol of alkyne)
involving 1a and 8f resulted in a yield of 62% of pure
white solid (10f), which was obtained by layering the
reaction mixture with hexanes. The remainder of the
solids obtained (from reduction of the toluene solution
and precipitation with hexanes) are slightly colored;
however, NMR analysis indicates the presence of 10f
and only small amounts of impurities consistent with
catalyst decomposition products. Although THF was
not a suitable solvent as a reaction medium (see below),
it has recently been found to be suitable for the isolation
of the products. The complete separation of catalyst
residue from all the pure products is currently being
investigated. Compounds 10c-f, 11g, and 14a have
been characterized by X-ray crystallography. The single-
crystal structural determinations of 10c,e and 14a are
presented in this work; details of the structures of 10d ,f
and 11g are given elsewhere.12
Sch em e 3
The products from the reactions of 1c with 8a and
8e have been reported,3 and our spectroscopic results
Sch em e 4
reagent (1 mol equiv), and ca. 5.7 × 10-6 mol (3 mol %)
of catalyst in 5 mL of toluene at 80 °C. Thus, completion
of the reaction constituted ca. 33 turnovers. Reaction
progress was monitored by GC/MS using 1 µL aliquots
removed hourly from the reaction vessel. In Scheme 3,
the approximate time to completion for each reaction
is listed in parentheses. For 8a ,c,f,g, using either 3b
or 4, reactions in toluene generally proceeded to comple-
tion within 3 h at 80 °C; however, for 8e the reactions
required about 20 h to reach completion. Reactions
involving 8b required extended periods of heating at 90
°C (33 h, 1a ; 50 h, 1c) to reach completion. Using the
alkyne 4-NCC6H4CtCH (8d ), reactions were incomplete
after several hours and additional catalyst (7 mol %
catalyst in all) and diboron reagent (ca. 1.5 equiv in all)
were required to reach completion. A total time of 75
h at 80 °C was required. Reactions using diboron
reagent 1b were significantly slower than with 1a ,
requiring, for example, >24 h for completion with alkyne
8g at 80 °C. These results confirm our premise regard-
ing the enhanced activity of the bis(phosphine)-
platinum complexes as catalyst precursors relative to
Pt(PPh3)4 (2). Both 3b and 4 showed significantly
greater activity than was reported3 for 2, even though
all reagents were considerably more dilute (by a factor
of ca. 10) in our experiments when similar alkynes were
employed.
The Bpin derivatives R1C(Bpin)dC(Bpin)R2 (11a -g)
are much more soluble than the respective Bcat ana-

5142 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
Sch em e 5
are in excellent agreement with those in the literature.
The H NMR spectra of 10f in CDCl3 obtained at 200
1
and 250 MHz exhibited only one broad resonance for
the aromatic hydrogen atoms. In C6D6, however, the
resonances attributed to the chemically distinct aro-
matic protons were resolved at 250 MHz.
The resonances in the 13C NMR spectra attributed to
carbon atoms bonded directly to boron ligands were not
observed in several cases, as noted in the Experimental
Section. This is due to the weak, broad nature of these
resonances which results from coupling with the qua-
drupolar boron nucleus. The broad resonances due to
chemically inequivalent boron nuclei also overlap in the
11B spectra of 10a -c and 11a -c.
Sch em e 6
As was found in previous reports,3 reactions with
C6H5CtCH (8b) were significantly slower than for other
alkynes, including 4-MeOC6H4CtCH (8c), and likewise,
in this study, those reactions involving C6H5CtCC6H5
(8e) were slower than with 4-MeOC6H4CtCC6H4OMe
(8g). The difference in reactivity of 8b vs 8c and 8e vs
8g is no doubt a result of the differences in the electron
density distributions in the CtCH and CtC moieties
caused by the presence of the π-donor OMe group. As
mentioned above, the catalytic diboration of π-acceptor-
substituted 4-NtCC6H4CtCH (8d ) with 1c was very
sluggish. The reaction was incomplete after 24 h
according to GC/MS results and required a total of 7
mol % catalyst and 75 h at 80 °C to reach completion.
Analysis of the 11B NMR spectrum of the crude product
indicated that a significant amount of B2(pin)3 (7) had
also formed. When the temperature was raised to 100
°C and 10 mol % of catalyst (3a for B2(cat)2, 4 for B2-
(pin)2) was employed, the reactions involving 8d were
significantly faster, requiring only 2 h to reach comple-
tion. NMR analysis of these crude reaction products
using diboron reagents 1a ,c indicated that only trace
amounts of B2(cat)3 (6) and B2(pin)3 (7) were formed,
respectively.
Ph(H)CdC(H)CtCPh (16; configuration unknown, m/ z
204 plus fragments) were also being formed (Scheme
5). The synthesis of [(PPh3)2Pt(η2-C6H5CtCH)] has
been described from both Pt(0) and Pt(II) precursors,13
and this compound has been shown to polymerize
phenylacetylene at 130 °C.14 This would account for the
formation of 16 and reduction of the observed rates
when compared to reactions involving 8e; however, the
stability of the alkyne complex is probably the main
source of the rate retardation observed in both cases.
The presence of π-donor substituents on the phenyl-
acetylene derivatives results in enhancement of the
observed rates of reaction, presumably due to the
destabilization of the [(PPh3)2Pt(η2-alkyne)] or [(PPh3)-
Pt(Bcat)2(η2-alkyne)] complex (vide infra). In contrast,
the presence of a π-acceptor substituent on the phenyl
ring of the alkyne drastically reduces the observed rates
of reaction, as would be expected due to the enhanced
stabilization of the Pt-alkyne bond.
Interestingly, by monitoring the reaction of 8h with
1c using GC/MS (Scheme 6), we observed the formation
of significant amounts of Me3SiBpin (18) and Me3-
SiCtCBpin (19), arising from CsSi bond cleavage,15 as
well as the expected diboration product Me3Si(Bpin)CdC-
Examination of the reactions involving the terminal
alkyne C6H5CtCH (8b ) and the internal alkyne C6-
H5CtCC6H5 (8e) indicates that the latter reacts at a
faster rate regardless of the diboron reagent used.
Monitoring the reaction of 8b with 1c by GC/MS
indicated that, in addition to the diboration product 11b,
small amounts of the butadiene-bis(boronate ester) Ph-
(H)CdC(H)C(Bpin)dC(Bpin)Ph (17; configuration un-
known, m/ z 458 plus fragments) and the ene-yne
(12) Clegg, W.; Scott, A. J .; Lesley, G.; Marder, T. B.; Norman, N.
C. Acta Crystallogr., in press.
(13) (a) Chatt, J .; Rowe, G. A.; Williams, A. A. Proc. Chem. Soc. 1957,
208. (b) Greaves, E. O.; Lock, C. J . L.; Maitlis, P. M. Can. J . Chem.
1968, 46, 3879. (c) McClure, G. L.; Baddley, W. H. J . Organomet. Chem.
1970, 25, 261.
(14) Furlani, A.; Collamati, I.; Sartori, G. J . Organomet. Chem. 1969,
17, 463.
(15) For a reference to cleavage of tCSi bonds by Pt, see: Ciriano,
M.; Howard, J . A. K.; Spencer, J . L.; Stone, F. G. A.; Wadepohl, H. J .
Chem. Soc., Dalton Trans. 1979, 1749.

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5143
(Bpin)SiMe3 (11h ) and the novel tris(boronate ester)
Me3Si(Bpin)CdC(Bpin)2 (20), the latter arising from the
diboration of 19. Apparently, following tCsSi oxidative
addition to the metal center, a metathetical reaction
with B2(pin)2 occurs, leading to SisB and tCsB
products. This is likely related to the stoichiometric
metallacyclopentane-B2(cat)2 reaction of Smith7a men-
tioned earlier. Similar behavior is apparent in reactions
involving 1a . The compound Me3SiBcat (21) was ob-
served as a significant product by GC/MS; however, the
1H NMR spectrum indicated the presence of several
additional products, presumably due to the metathetical
reactions described. The isolation of the individual
reaction components is still being examined. It has also
been reported that reactions between 3a and Me3-
SnSnMe3 or [(PPh3)2Pt(SnMe3)2] and 1a both proceed
irreversibly to Me3SnBcat.7b These results give further
evidence for the presence of metathetical reactions
involving 1a and 1c and are consistent with the
observation of products derived from the tCsSi bond
cleavage in 8h by the Pt catalyst.
Suzuki, Miyaura, et al. reported3 that polar solvents,
especially DMF, accellerated the alkyne diboration
reaction using B2(pin)2 and Pt(PPh3)4. Thus, we exam-
ined the effect of solvent binding to 1a ,c and 10e in
CDCl3 with various concentrations of DMF using 11B
NMR. The addition of 2 molar equiv of DMF with
respect to 10e resulted in an upfield shift in the
resonance from 31.8 to 23.2 ppm, indicative of signifi-
cant binding to Bcat groups in (Z)-PhC(Bcat)dC(Bcat)-
Ph. Only a slight shift in the resonance was observed
for 1a in the presence of 2 molar equiv of DMF; however,
the addition of 50 molar equiv of DMF resulted in a shift
of ca. 6 ppm. In contrast, the addition of up to 50 molar
equiv of DMF to a solution of 1c resulted in no
significant shift in the 11B NMR resonance. This is
consistent with the greater Lewis acidity of Bcat com-
pounds compared with their Bpin analogues16 and of
the vinyl-bis(boronate esters) compared with the dibo-
ron reagents. The reported influence of DMF on reac-
tion rates remains unexplained.
Qu a lita tive Kin etic Exa m in a tion . A series of in
situ 1H NMR experiments were conducted at 52 °C in
CDCl3 solution using 0.113 mmol of alkyne, 0.130 mmol
of diboron reagent, and 5-6 mol % of catalyst. Reaction
of 1a with 8a in the presence of either 3b or 4 proceeded
to ca. 50% conversion within 30 min and was complete
within ca. 4 h. The same reaction using 1c reached only
50% conversion after 5 h. The relative rates for the
three diboron reagents were found to be 1a > 1c > 1b.
Thus, our premise that 1a would be more efficient than
1c was also verified. The reason for the low activity of
1b is not clear at this time. Furthermore, addition of 2
equiv of PPh3 to 4 greatly decreased the rate of the
catalyzed diborations, consistent with our postulate that
the active catalyst was unlikely to possess more than
two bound phosphine ligands. In fact, it would appear
that PPh3 dissociation from the bis(phosphine) catalyst
precursors is critical. The progress of the above reac-
tions was determined from a comparison of the inte-
grated areas of resonances attributed to the CtCCH2
and CdCCH2 moieties. Initially, plots of ln[alkyne] vs
time were linear, indicating overall first-order kinetics;
however, in the latter stages of the reactions, curvature
was apparent which is attributed to the partial decom-
position of the catalyst in CDCl3 as described below.
Given the fact that the initial concentrations of alkyne
and diboron were equal and that they are disappearing
at the same rate, the observed first-order disappearance
of alkyne implies that the reaction is actually first order
in the product of alkyne and diboron concentration, i.e.
[alkyne]n[diboron]m, where n + m ) 1. Recently, Iver-
son and Smith7b have performed detailed kinetic studies
of both stoichiometric and catalytic variants of the
reaction with B2(cat)2 (1a ) using 4-octyne. Under
catalytic conditions, in the presence of added PPh3, the
authors observed a first-order dependence on [alkyne],
a zero-order dependence on [diboron], and an inverse
first-order dependence on [PPh3], which is consistent
with the behavior found in our study.
In a separate series of experiments, under similar
reaction conditions (CDCl3, 52 °C), however, the addition
of 4 molar equiv of 1a also reduced the rate of the
reaction significantly. The reason for this is unclear;
however, the possibility that an alternative mechanistic
pathway involving decomposition of 3a or 1a or revers-
ible oxidative addition of 1a to 3a seemed reasonable.
To test the latter hypothesis, a sample containing
equimolar amounts of 3b and 1a was heated in toluene
for 3 h. The solvent was then removed in vacuo, and
the crude residue was dissolved in CDCl3 and analyzed
by multinuclear NMR. The proximity and broad char-
acter of the resonances in the 31P and 11B NMR spectra
do not allow a differentiation between 3a and 3b, as
the resonances are overlapped. The 1H NMR spectrum,
however, in the region of the tert-butyl groups, displayed
resonances due to the presence of free 1b (δH 1.36 ppm),
as well as that for 3b (δH 1.20 ppm), indicating the
presence of an equilibrium between 3a and 3b which
favors the production of 3a to a very slight degree. No
additional resonances were present to suggest the
formation of either mixed B-B compounds or Pt-bis-
(boryl) compounds containing two different types of
boryl ligands. Thus, the most likely process for the
exchange of the boryl ligands (at least under these
conditions) involves B-B reductive elimination and then
B-B oxidative addition (Pt(II) f Pt(0) f Pt(II)) rather
than B-B oxidative addition and then B-B reductive
elimination (Pt(II) f Pt(IV) f Pt(II)), as the latter
might be expected to lead to boryl group scrambling.
Mech a n istic Deta ils. In reactions involving 5a ,b
no catalytic activity for the addition of 1a to 8a at 52
°C in CDCl3 was observed. Similar behavior was
apparent in the reaction involving the internal alkyne
8g, in toluene at 80 °C using 5a , which showed no
activity over 66 h. Interestingly, under the same
conditions (i.e. toluene, 80 °C), the reaction proceeded
to greater than 90% completion after a period of 2 weeks
when 5b was employed as the catalyst precursor.
Clearly, a trans-(PPh3)2Pt(Bcat)2 isomer is not the
catalytically active species in these reactions, and it
seems highly likely that phosphine dissociation even
from the bis(phosphine) complexes is required. This
result provides additional insight into the mechanism
of these catalytic reactions first proposed by Miyaura
and Suzuki and co-workers.3a While the present work
was in progress, Iverson and Smith reported7a that 3a
reacts stoichiometrically with 4-octyne in the presence
of 1.5 mol equiv of 1a to give the 1,2-vinyl-bis(boronate
ester) diboration product and 3a . These authors also
(16) Nguyen, P.; Dai, C.; Taylor, N. J .; Power, W. P.; Marder, T. B.;
Pickett, N. L.; Norman, N. C. Inorg. Chem. 1995, 34, 4290.

5144 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
Sch em e 7
equilibrium between compounds 3a -c and a mono-
(phosphine) species lies well on the side of the bis-
(phosphine) complexes.
In the presence of PPh3, Iverson and Smith reported7b
that 3a shows no reaction, while 3c exists in an
equilibrium with Pt(PPh3)4 (2) and B2(pin)2. Alterna-
tively, the reaction of 3c with B2(cat)2 proceeds irrevers-
ibly to 3a and B2(pin)2. This reversibility of the B-B
bond activation which was observed could contribute to
the reduced rates associated with catalytic reactions
involving B2(pin)2 reported in this work and elsewhere.3
In addition, this presumably accounts for the require-
ment that a large excess of B2(pin)2 be present for the
isolation of 3c when it is synthesized from Pt(PPh3)4
(2).3
Ca ta lytic Ad d ition of B-B Bon d s to 1,3-Diyn es.
The addition of 2 equiv of B2(cat)2 (1a ) to 4-MeO-
C6H4CtCCtCC6H4-4-OMe (9a ) proceeded smoothly to
give the novel tetrakis(boronate ester) compound (Z,Z)-
(4-MeOC6H4)C(Bcat)dC(Bcat)C(Bcat)dC(4-MeOC6H4)-
(Bcat) (14a ) within 3 h using catalyst precursor 3b or 4
(Scheme 4). Again, the addition of PPh3 to the reaction
catalyzed by 4 greatly reduced the rate of the reaction.
Attempts to isolate the intermediate (Z)-(4-MeOC6H4)C-
(Bcat)dC(Bcat)CtC-(4-MeOC6H4) (12a ) using 1 equiv
of 1a were unsuccessful, as mixtures of 12a , 14a , and
unreacted diyne 9a were observed, indicating that the
second addition occurs at a rate similar to the first
addition of diboron reagent. The reaction of 1a with
Me3SiCtCCtCSiMe3 (9b), on the other hand, was very
slow. Examination of GC/MS data revealed that the
diyne was still present even after ca. 40 h. We were
unable to detect the presence of the intermediate
compound Me3SiCtCC(Bcat)dC(Bcat)SiMe3 (12b) by
GC/MS, and thus, the extent of the reaction could not
be determined. As a result, the toluene reaction mix-
ture was layered with hexanes and cooled to -36 °C,
resulting in the formation of a white precipitate. The
1H and 13C NMR spectra of this product, however, were
complex, indicating a variety of products which could
not be characterized unambiguously.
reported that the alkyne complex [(PPh3)2Pt(η2-4-oc-
tyne)] reacted with 1a to generate 3a with loss of alkyne,
indicating that the initial step in the mechanism of
these reactions involves the oxidative addition of B-B
rather than the coordination of alkyne to the metal.
Scheme 7 illustrates a more detailed description of
the proposed mechanism involved in the catalytic dibo-
ration of alkynes. The first step is rapid and involves
the formation of the oxidative-addition product (3). This
can be accomplished by reaction of 1a or 1c with 4 or,
alternatively, with 3b as discussed above. The fact that
3b was more stable than 3a in initial attempts to isolate
the oxidative addition products led to its initial choice
as a catalyst precursor; however, isolated samples of 3a
have been examined and were found to exhibit similar
catalytic activity. The next step in the catalytic cycle
should involve the dissociation of a phosphine ligand
and association of the alkyne, as it has been shown that
the addition of PPh3 or the presence of a more strongly
bound bidentate phosphine inhibits the reaction. This
Addition of the first equivalent of B2(pin)2 (1c) to
diyne 9a was rapid to give (Z)-(4-MeOC6H4)C(Bpin)dC-
(Bpin)CtC(4-MeOC6H4) (13a ), whereas addition of the
second equivalent of 1c to produce (Z,Z)-(4-MeOC6H4)C-
(Bpin)dC(Bpin)C(Bpin)dC(4-MeOC6H4)(Bpin) (15a) was
sluggish. This allowed for the preparation and charac-
terization of the intermediate species 13a from the
reaction of 9a with 1 equiv of 1c (Scheme 4). The
unsymmetrical nature of the product formed gives rise
to two resonances for the chemically inequivalent meth-
1
intermediate has not been detected, although H NMR
studies in CDCl3 do indicate the presence of resonances
attributable to cis-[(PPh3)2Pt(B(OR))2] throughout the
course of the reaction. This may be an indication that
the bis(phosphine) bis(boryl) complex is the catalyst
resting state and that alkyne binding or alkyne insertion
into the metal-boryl bond may be rate-determining
(vide infra). The reductive elimination of the diborated
olefin product is probably rapid and completes the
catalytic cycle. The role of phosphine in the latter
stages of the catalytic cycle is unknown. Either the
phosphine can add to the metal center upon reductive
elimination of the product or the mono(phosphine)
complex may add another 1 equiv of diboron reagent
and continue the catalytic cycle. As we do not observe
free PPh3 in NMR spectra of solutions of 3a -c, and the
broad nature of the 31P NMR resonances can be at-
tributed to coupling with 11B, it would appear that the
1
oxy groups, as expected, in the H (3.80, 3.75 ppm) and
13C (55.1, 55.0 ppm) NMR spectra. In the preparation
of 15a , GC/MS analysis indicated that small amounts
of diyne 9a remained after 3 h; therefore, the reaction
mixture was left for 16 h to ensure completion. The
symmetric tetrakis(boronate ester) product displays a
resonance for only one chemically distinct methoxy
group (δH 3.73 ppm; δC 55.1); however, there are four
distinct resonances for the CH3 groups of the Bpin
moieties in the 1H and 13C NMR spectra. Initial
molecular mechanics calculations on a model for 15a
indicate that hindered or geared rotation of the Bpin
groups occurs, giving rise to four separate signals in this
1
region of the H NMR spectrum (1.29, 1.24, 1.00, 0.94

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5145
F igu r e 5. Molecular structure of (E)-(4-MeO-C6H4)C-
(B(1,2-O2C6H4))dCH(B(1,2-O2C6H4)) (10c), with 50% prob-
ability ellipsoids.
ppm). This is also apparent in the 13C NMR spectrum,
in which there are two quaternary carbons present
(83.0, 82.9 ppm) and four resonances in the region for
primary carbon atoms associated with the CH3 groups
of the Bpin moiety (25.2, 24.8, 24.5, 24.3 ppm). Thus,
the (Bpin)4 compounds are quite sterically encumbered.
The reaction involving bis(trimethylsilyl)butadiyne
(9b) and 1c was very slow, consistent with results from
the reaction involving 1a . Monitoring the reaction by
GC/MS indicated that the reaction proceeded to form
the intermediate bis(boronate ester) (Z)-Me3SiC(Bpin)dC-
(Bpin)CtCSiMe3 (13b) prior to the subsequent reaction
to produce the tetrakis(boronate ester) (Z,Z)-Me3SiC-
(Bpin)dC(Bpin)C(Bpin)dC(Bpin)SiMe3 (15b). This lat-
ter step required a reaction time of 77 h to reach
completion. The extent of the reaction in this case could
be determined by GC/MS by monitoring the disappear-
ance of compounds 13b and 1c. As with the preparation
of 14b, NMR data could not be assigned due to the
presence of products derived from the CtCSiMe3 meta-
thetical reactions described above. The preparation of
13b involving only 1 equiv of 1c required a reaction time
of 6 h to reach completion, and the absence of meta-
thetical reactions allowed for complete NMR character-
ization. The mass of the parent ion M+ for the tetrakis-
(boronate esters) 14a ,b and 15a ,b exceeds the mass
range of the GC/MS (650 amu) used in these investiga-
tions; however, compounds 15a ,b have been identified
(M + H+) by directly introducing samples into the
electrospray unit of an HPLC/MS/MS spectrometer, as
described in the Experimental Section. Interestingly,
peaks attributable to (15b + nH2O + H+) (n ) 0-4)
were observed (aqueous CH3CN was employed in the
analysis), indicating that 15b is stable to H2O and is
also capable of binding up to four molecules of water.
Molecu la r Str u ctu r es of Or ga n obor on a te Ester s.
The structure of (E)-(4-MeO-C6H4)C(Bcat)dCH(Bcat)
(10c; Figure 5) represents the first structural evidence
of the cis disposition of the boron substituents in the
products derived from the catalytic diboration of a
terminal alkyne. The CdC bond distance (1.348(2) Å)
is typical for olefin compounds and is similar to or
shorter than the respective CdC bond distances in the
internal alkene and diene derivatives (10e (two crys-
tallographically independent molecules in the unit cell),
1.353(2) and 1.358(2); 10f, 1.357(2); 11g, 1.358(2); 14a ,
1.373(3) and 1.362(2) Å). Replacement of the methoxy
functionality with a cyano group results in no significant
changes in the CdC distance (10d , 1.349(2) Å). The
F igu r e 6. Molecular structure of (Z)-(C6H5)C(B(1,2-
O2C6H4))dC(C6H5)(B(1,2-O2C6H4)) (10e), with 50% prob-
ability ellipsoids. One of the two similar but independent
molecules is shown.
C(1)-B(9) bond distance (1.526(2) Å) is also smaller
when compared to the C(2)-B(18) bond distance (1.566(2)
Å) and those in the other Bcat derivatives described
(10d , 1.569(2), 1.535(2); 10e, 1.559(2), 1.551(2), 1.553(2),
1.562(2); 10f, 1.565(2), 1.553(2); 14a , 1.541(3), 1.570(3),
1.565(3), 1.546(3) Å). Both deviations are presumably
due to the decrease of steric repulsion present at the
terminal carbon atom. The B-C bond distances for 11g
(1.580(2) and 1.564(2) Å) are slightly larger due to the
steric constraints of the Bpin functional group. The
structures of 10d ,f and 11g are similar to that of 10e
and will not be discussed in detail in this report.12
Relief of steric congestion at the terminal carbon atom
in 10c is also apparent in the bond angles, with the
angle formed by B(9)-C(1)-C(2) (124.4(1)°) being larger
than any of the other sp2-hybridized bond angles (C(1)-
C(2)-C(3), 123.6(1)°; C(1)-C(2)-B(18), 120.1(1)°; B(18)-
C(2)-C(3), 116.3(1)°) in the structure. The decrease in
the B(18)-C(2)-C(3) angle also indicates that the boryl
moieties on adjacent carbon atoms of the olefin have a
slightly larger influence than the aryl counterparts in
determining the steric requirements in the solid-state
structure of this compound and that this depends upon
the CdC(boryl) rotational conformation. The interpla-
nar angle between the mean plane formed by the aryl
carbons, C(3)-C(8), and the mean plane formed by B(9),
C(1), C(2), C(3), B(18) is 16.9°, and the planes formed
by the boryl ligands subtend interplanar angles of 7.0
and 83.9° ((B(9), O(10), O(11), C(12)-C(17) and B(18),
O(19), O(20), C(21)-C(26), respectively) with respect to
the C3B2 alkene plane. This results in the aryl group
and one Bcat ligand being almost coplanar with the
alkene mean plane while the other Bcat ligand is almost
perpendicular due to steric constraints.
The structure of (Z)-(C6H5)C(Bcat)dC(Bcat)(C6H5)
(10e; Figure 6) represents the first structural evidence
of the cis disposition of the boron substituents in the
products derived from the catalytic diboration of an
internal alkyne. In this structure, the CdC and BsC
bond lengths in the two crystallographically indepen-
dent molecules correlate well, although there are sig-

5146 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
and (C(61)-C(66)) display very similar interplanar
angles of 57.6, 18.3, and 66.1°, respectively, in relation
to the mean plane defined by C(3), C(4), B(3), B(4), C(2),
and C(61). Thus, boryl ligands in the 1- and 4-positions
are nearly coplanar with their CdC unit, whereas boryl
ligands in the 2- and 3-positions are closer to a perpen-
dicular orientation, as are the aryl rings.
Decom p osition of Ca ta lysts. The completion of the
catalytic reactions in toluene (80 °C) was accompanied
by a noticeable change in color of the solutions, usually
to a deep red color associated with the decomposition
of the catalyst. When slight excesses of B2(cat)2 or B2-
(pin)2 were used, very minute resonances due to the
presence of B2(cat)3 (6)17 or B2(pin)3 (7)18 were also
detected in the 1H, 11B, and 13C NMR spectra of the
crude reaction mixtures. In addition, relatively large
amounts of 6 or 7 could be observed in the spectra of
reactions requiring extended reaction times, such as
those involving π-acceptor-substituted alkynes, in which
additional diboron reagent was required to complete the
catalytic reaction. As well, the in situ spectra recorded
during the formation of 3c also exhibited resonances in
the 11B{1H} NMR spectrum consistent with the forma-
tion of B2(pin)3 (7). It seemed unlikely that the initially
reported value for 3c (δB 21.50 ppm)3a was due to the
presence of an oxidative-addition product as originally
proposed, but rather, we believe that this sharp reso-
nance corresponds to the byproduct 7. Recent reports
by the same authors3b have provided a new value (δB
46.3 ppm) for 3c which is consistent with those obtained
for similar compounds described in this work. Recently,
related research in our laboratory has resulted in the
isolation of authentic 7 (δB 21.7 ppm)18 confirming (by
single-crystal X-ray diffraction) the nature of this
compound. In addition, 7 is formed in the reaction of 2
equiv of BH3 with 3 equiv of pinacol (albeit in low yield)
and has also been identified as a common byproduct in
the synthesis of 1c. In the latter case, recrystallization
from hexanes resulted in pure samples of 1c. It seemed
apparent, therefore, that the subsequent decomposition
of catalyst was intimately related to the formation of 6
or 7. A series of in situ NMR experiments were
performed to investigate the stability of the catalysts,
the effect of solvent on the decomposition, and the
reaction between B2(cat)3 (6) and (PPh3)2Pt(η-C2H4) (4).
In the absence of excess B2(cat)2 (1a ) or alkyne,
solutions of 3a in CDCl3 began to decompose within 1
h. After 1 week, new resonances were apparent in the
1H, 11B{1H}, and 31P{1H} NMR spectra. The 31P{1H}
NMR spectrum indicated the presence of two major
compounds with the same (within experimental error)
chemical shifts but with differing J Pt-P coupling con-
stants (δP 28.7 ppm; J Pt-P ) 1634 and 3021 Hz). The
hydride region of the 1H NMR spectrum exhibited a
triplet at -16.3 ppm (J P-H ) 13 Hz, J Pt-H ) 1197 Hz).
The remaining portion of the 1H NMR spectrum dis-
played several overlapping resonances in the aromatic
region consistent with PPh3- and Bcat-containing com-
pounds. These results are consistent with the presence
of 3a and the formation of trans-(PPh3)2Pt(H)(Cl), which
has been characterized previously.19a-c The nature of
this compound has been determined unambiguously by
means of X-ray crystallography.19d,e The 11B{1H} NMR
F igu r e 7. Molecular structure of (Z,Z)-(4-MeO-C6H4)C-
(B(1,2-O2C6H4))dC(B(1,2-O2C6H4))C(B(1,2-O2C6H4))dC(4-
Me-OC6H4)(B(1,2-O2C6H4)) (14a ), with 50% probability
ellipsoids.
nificant differences in some of the bond angles. In
molecule 1, the C(31)-C(1)-B(1) and C(41)-C(2)-B(2)
angles are reduced from 120 to 111.84(12)° and
116.91(13)°, respectively, whereas the angles formed by
B(1)-C(1)-C(2) (126.51(14)°) and C(31)-C(1)-C(2)
(121.64(13)°) are greater than 120°. In molecule 2, the
bond angles around C(51), namely, B(3)-C(51)-C(81)
) 119.29(13)°, B(3)-C(51)-C(52) ) 119.28(14)°, and
C(81)-C(51)-C(52) ) 121.43(14)°, indicate that the
steric requirements in the solid state may be relieved
by changes in the interplanar angles of the boryl and
aryl functional groups, as values are approaching that
expected for pure sp2 hybridization. Clearly, some
balance must exist between the steric effects of the
groups on adjacent olefinic carbon atoms and the
interplanar angles formed by these groups. This is also
evident in the bond angles formed in the other half of
molecule 2, which are closer to typical values found in
molecule 1 (B(4)-C(52)-C(91) ) 111.03(12)°; B(4)-
C(52)-C(51) ) 125.23(14)°; C(91)-C(52)-C(51) )
123.58(14)°). Interplanar angles of 76.3° (B(1), O(1),
O(2), C(11)-C(16)), 10.9° (B(1), O(1), O(2), C(11)-C(16)),
55.9° (C(31)-C(36)), and 57.7° (C(41)-C(46)) are formed
with respect to the mean plane defined by C(1), C(2),
B(1), B(2), C(31), and C(41) in molecule 1. In molecule
2, the boryl groups form interplanar angles of 4.6° (B(3),
O(5), O(6), C(61)-C(66)) and 77.5° (B(4), O(7), O(8),
C(71)-C(76)) while the aryl groups form angles of 56.7°
(C(81)-C(86)) and 54.3° (C(91)-C(96)) with respect to
the mean plane defined by C(51), C(52), B(3), B(4),
C(81), C(91).
The structure of (Z,Z)-(4-MeOC6H4)C(Bcat)dC(Bcat)-
C(Bcat)dC(4-MeOC6H4)(Bcat) (14a ; Figure 7) is the first
determined for a butadiene tetrakis(boronate ester) and
demonstrates the cis disposition of the boron substitu-
ents in the products derived from the catalytic tetrabo-
ration of an internal diyne. This compound crystallizes
in the s-trans conformation with a torsion angle of
150.7° with respect to C(1), C(2), C(3), and C(4), but the
bond angles displayed in the structure deviate only
slightly from 120°. The interplanar angles formed with
respect to the mean plane defined by C(1), C(2), B(1),
B(2), C(31), and C(3) are 18.6° (B(1), O(1), O(2), C(11)-
C(16)), 66.5° (B(2), O(3), O(4), C(21)-C(26)), and 58.4°
(C(31)-C(36)) and the mean planes formed by (B(3),
O(6), O(7), C(41)-C(46)), (B(4), O(8), O(9), C(51)-C(56)),
(17) Westcott, S. A.; Blom, H. P.; Marder, T. B.; Baker, R. T.;
Calabrese, J . C. Inorg. Chem. 1993, 32, 2175.
(18) Clegg, W.; Scott, A. J .; Dai, C.; Lesley, G.; Marder, T. B.;
Norman, N. C.; Farrugia, L. J . Acta Crystallogr., in press.

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5147
spectrum exhibited only one new resonance at 23.7 ppm,
which is consistent with the formation of B2(cat)3 (6) in
CDCl3.17
and cis-(PPh3)2PtCl2 (δP 14.7 ppm; J Pt-P ) 3675 Hz)24
and new resonances at 26.5 ppm (s, J Pt-P ) 3187 Hz),
19.7 ppm (d, J ) 17 Hz), and 17.6 ppm (d, J ) 17 Hz).
The resonance at 26.5 ppm was the most abundant of
the new resonances formed and is attributed to the
formation of solvated (PPh3)2Pt from ethylene dis-
sociation.20d The 1H NMR spectrum also exhibited a
resonance due to free ethylene at 5.2 ppm. Previous
reports for the isolation of the compound (PPh3)2Pt
indicated20b that the compound was yellow, which is
consistent with the change in color of the solution noted
in this work. It is unfortunate that no 31P chemical
shifts were reported by the authors to enable a com-
parison on this basis. The pair of doublets observed
could be due to cis-(PPh3)2Pt(H)(CCl3), which would be
consistent with the observed multiplicity of the reso-
nances and reaction with solvent. This compound is
very unstable in solution and disappears over time.
Minute resonances in the form of four broad multiplets
In contrast, C6D6 solutions of 3a are stable for long
periods of time at room temperature. After 4 weeks,
the 31P{1H} NMR spectrum indicated the presence of
3a (δP 29.8 ppm; J Pt-P ) 1622 Hz) and a new resonance
at 24.2 ppm (J Pt-P ) 2900 Hz). The nature of this new
product is not known; however, the 11B{1H} NMR
spectra did indicate that significant quantities of B2-
(cat)3 (6) were present (δB 22.4 ppm in C6D6). Solutions
of 3a in C6D6/THF were observed to decompose more
rapidly compared to those in CDCl3 or C6D6. Although
the reason for this is uncertain, the use of THF as a
solvent for the catalytic reactions was avoided.
The results in CDCl3 indicated that a reaction was
occurring between the Pt center and the solvent, as this
was the only source of Cl available. To determine the
role of the boryl groups in this decomposition, we
examined the in situ decomposition of (PPh3)2Pt(η-C2H4)
(4) in both CDCl3 and C6D6, as this would give an
indication of which products could be forming from
interactions involving the (PPh3)2Pt fragment and sol-
vent.
The in situ 31P{1H} NMR spectrum of a C6D6 solution
of 4 (δP 34.9 ppm; J Pt-P ) 3741 Hz) indicated no
noticeable changes over a period of 2 h. A CDCl3
solution of the same sample of 4, however, exhibited
resonances attributable to at least two different Pt-Cl-
containing compounds. The behavior in solution of 4
and related Pt(0) compounds such as (PPh3)3Pt and
(PPh3)2Pt have been studied extensively.20-22 Malatesta
and Cariello reported20a that samples of (PPh3)3Pt
undergo dissociation in solution and first proposed the
formation of a (PPh3)2Pt species to account for the
behavior observed. Ugo et al. reported20b the synthesis
of (PPh3)2Pt by several routes and subsequently pro-
posed the formation of a trimeric cluster20c to account
for the red compounds formed upon heating of the
(PPh3)2Pt sample. Glockling and co-workers,21 upon
studying reactions of 4, reformulated this trimeric
cluster and related decomposition products as arising
from ortho-metalation reactions involving the phosphine
ligands. Subsequent to this report, Carty et al.22a
reported structural evidence of facile P-C bond cleav-
age23 giving rise to phosphido-bridged Pt clusters which
arise by refluxing solutions of (PPh3)4Pt (2). In this
study, 31P{1H} NMR analysis of the yellow solution
formed initially indicated the presence of 4 (δP 34.4 ppm;
J Pt-P ) 3718 Hz), trans-(PPh3)2Pt(H)(Cl) (δP 28.7 ppm),
1
were also present in the hydride region of the H NMR
spectrum (ca. -3 to -5 ppm) which are consistent with
the formation of an additional hydrido-platinum com-
pound. The possibility of the formation of cis-(PPh3)2-
Pt(H)(Cl) seemed unlikely, since the trans isomer has
been shown to be the only isomer present in solution.25
As mentioned above, the formation of B2(cat)3 (6) and
B2(pin)3 (7) in catalytic reactions (toluene, 80 °C) involv-
ing π-acceptor-substituted alkynes such as 8d indicated
that alternative reactions involving the diboron reagent
and/or catalyst may be occurring in solution. We
decided, therefore, to examine the reaction between 6
and 4. These reactions were followed by in situ NMR
spectroscopy in CDCl3 and C6D6.
In CDCl3, the 31P{1H} NMR spectrum indicated the
formation of a large quantity of trans-(PPh3)2Pt(H)(Cl)
when compared to the decomposition of 4 alone. The
addition of 6 to the solution clearly enhanced the
formation of this hydrido-platinum compound. In
addition, the formation of resonances assigned above as
(PPh3)2Pt and cis-(PPh3)2PtCl2 were also apparent. Two
additional resonances (δP 23.6 and 29.9 ppm) which
were not present in the decomposition of 4 or 3a did
appear. The resonance at 23.6 ppm (J Pt-P ) 2870 Hz)
has been assigned to the compound trans-(PPh3)2Pt(Cl)-
(Bcat).26 The nature of the compound corresponding to
the resonance at 29.9 ppm is not certain; however, the
solution was observed to turn dark red. Solutions of 4
in CDCl3 were initially yellow and became red only after
extended periods of time. The compound trans-(PPh3)2-
Pt(Cl)(Bcat) is a colorless compound when pure; there-
fore, the red color observed may correspond to the
compound giving rise to this new, unassigned resonance.
As mentioned, the formation of ortho-metalation prod-
ucts or polymetallic complexes derived from facile P-C
bond cleavage giving rise to bridging phosphido clusters
has been proposed to account for the products obtained
as red solutions. The 31P spectra of these compounds,
however, are expected to be more complex due to the
presence of the inequivalent phosphine ligands which
would be formed by either process. No resonances due
(19) (a) Chatt, J .; Shaw, B. L. J . Chem. Soc. 1962, 5075. (b) Ugo,
R.; LaMonica, G.; Cariati, F.; Cenini, S.; Conti, F. Inorg. Chim. Acta
1970, 4, 390. (c) McFarlane, W. J . Chem. Soc., Dalton Trans. 1974,
324. (d) Bender, R.; Braunstein, P.; J ud, J .-M.; Dusausoy, Y. Inorg.
Chem. 1984, 23, 4489. (e) Lesley, G.; Marder, T. B.; Scott, A. J .; Clegg,
W.; Norman, N. C., unpublished results.
(20) (a) Malatesta, L.; Cariello, C. J . Chem. Soc. 1958, 2323. (b) Ugo,
R.; Cariati, F.; LaMonica, G. Chem. Commun. 1966, 868. (c) Gillard,
R. D.; Ugo, R.; Cariati, F.; Cenini, S.; Bonati, F. Chem. Commun. 1966,
869. (d) Cook, C. D.; J auhal, G. S. Can. J . Chem. 1967, 45, 301.
(21) Glockling, F.; McBride, T.; Pollock, R. J . I. J . Chem. Soc., Chem.
Commun. 1973, 650. For related reactions involving Ir see: Bennett,
M. A.; Milner, D. L. J . Am. Chem. Soc. 1969, 91, 6983.
(22) (a)Taylor, N. J .; Cheih, P. C.; Carty, A. J . J . Chem. Soc., Chem.
Commun. 1975, 448. (b) In further work by this group, the 31P{1H}
NMR spectrum (toluene-d8) of (PPh3)2Pt2(µ-PPh2)2, which was the
major decomposition product observed by a variety of synthetic routes,
was reported: δ 163.3 ppm (a series of triplets, PPh2), 28.3 (intense
multiplet, PPh3). Hartstock, F. W. M.Sc. Thesis, University of Waterloo,
1981. This compound was characterized as being only sparingly soluble
in common NMR solvents.
(23) (a) Patel, H. A.; Fischer, R. G.; Carty, A. J .; Naik, D. V.; Palenik,
G. J . J . Organomet. Chem. 1973, 60, C49. (b) Cullen, W. R.; Harbourne,
D. A.; Liengme, B. V.; Sams, J . R. Inorg. Chem. 1970, 9, 702.
(24) See for example: Al-Najjar, I. Inorg. Chim. Acta 1987, 128, 93
and references therein.
(25) Collamati, I.; Furlani, A.; Attioli, G. J . Chem. Soc. A 1970, 1694.
(26) Lesley, G.; Marder, T. B.; Scott, A. J .; Clegg, W.; Norman, N.
C., unpublished results.

5148 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
to bridging phosphido groups were observed.22b The
resonance observed in this work (29.9 ppm) would be
more consistent with a polymeric cluster involving
(PPh3)2Pt vertices similar to the compounds initially
proposed by Ugo et al.,20c in which the phosphine ligands
are chemically and magnetically equivalent.
(pin)2. In this regard, the authors indicated that the
possibility of an associative pathway involving the
reaction of the Pt-alkyne compound with 1c could not
be ruled out. In addition, the same authors noted that
kinetic investigation of stoichiometric and catalytic
reactions involving 1a and 3a were first order in catalyst
concentration, under pseudo-first-order conditions in
alkyne concentration. The fact that (PPh3)2Pt(Bpin)2
(3c) undergoes reductive elimination indicated that
reactions with CDCl3 may significantly reduce the
concentration of the catalyst and, thus, the rate of the
reaction when comparing kinetic results from reactions
involving 1a and 1c. This may contribute to the reduced
rates observed in our initial kinetic studies with 1-oc-
tyne (8a ) and B2(pin)2 (1c), as 4 was employed as the
catalyst. As mentioned above, comparisons in this study
were drawn from initial portions of plots of ln[alkyne]
vs time, which were linear for reactions involving 1a
and 1c. Deviations from linearity at the latter stages
of the reactions were apparent in the presence of 1a or
1c, and also, when 1c was used as the diboron reagent,
the deviation was more pronounced.
In the reaction of 6 with 4 in C6D6, an insoluble red
oil formed rapidly, accompanied by the appearance of a
1
new hydride resonance in the H NMR spectrum (t, δH
-23.2 ppm; J P-H ) 13.7 Hz; J Pt-H ) 1359 Hz). The 31P-
{1H} NMR spectrum also exhibited new resonances at
30.6 ppm (J Pt-P ) 3061 Hz) and 23.1 ppm (minor
product, no Pt satellites were observed) in addition to
4. The resonance at 30.6 ppm may be the result of the
formation of polymetallic compounds as noted above, as
a red product was observed to form and the chemical
shift is quite similar to the one observed in CDCl3 at
29.9 ppm (a slight downfield shift is also present in
changing solvent from CDCl3 to C6D6 for samples of 4).
The value of the Pt-P coupling constant for the reaction
in CDCl3 could not be determined for comparison. The
remaining resonance at 23.1 ppm would, therefore,
represent a hydrido-platinum species corresponding to
The decomposition noted above does not appear to
interfere with the catalysis in toluene at 80 °C with the
above-noted exceptions. It is clear that the choice of
solvent and purity of the diboron reagents (i.e. absence
of any B2(cat)3 and B2(pin)3 in the synthesis of 1a and
1c, respectively) are crucial to accurately determine the
kinetic behavior of these systems. It should be noted
that the samples of B2(cat)2 and B2(pin)2 used in this
study were rigorously purified and that their purity was
checked carefully prior to use.
1
the hydride resonances observed in the H NMR spec-
trum. The formation of this complex is also enhanced
by the addition of 6 when compared to the decomposition
of 4 in the absence of 6 in C6D6. The origin and nature
of this species are uncertain. The possibility of ortho-
metalation reactions, similar to those mentioned above,
cannot be ruled out. Hartwig et al.27 have recently
demonstrated the photolytic activation of benzene and
toluene by CpFe(CO)2(Bcat). However, the observation
of a hydride signal in C6D6 would preclude the solvent
as the source of the hydride in our case. It seemed
unlikely that (PPh3)2Pt(H)(Bcat) could be responsible for
the appearance of the new hydride resonance, since
preliminary studies26 involving HBcat and 4 indicate
the rapid formation of 3a , accompanied by the evolution
of H2. The instability of (PPh3)2PtH2 compounds has
been reported,28 and it is unlikely that this compound
is stable enough to be attributed to this resonance.
In addition to the solution behavior mentioned above,
11B NMR spectra for the reactions in both solvents
exhibited minor resonances consistent with the forma-
tion of [B(cat)2]-. The formation of this compound may
arise due to self-ionization of B2(cat)3 (heterolytic B-O
bond cleavage) or, alternatively, as a result of reactions
involving the metal center and B2(cat)3. It seems likely
that the unassigned resonances mentioned above could
also arise from B-O bond cleavage or ionic reactions
involving boron, occurring at the metal center. It is
clear that the formation of hydrido-platinum com-
pounds is enhanced by the addition of B2(cat)3, and it
would appear that the process occurring also involves
solvent interactions, at least in CDCl3. The exact nature
of this process remains undefined and will be investi-
gated in more detail.
Con clu sion s
We have shown that (PPh3)2Pt complexes, either Pt-
(II) bis(boryls) or Pt(0)-ethylene complexes, are more
efficient catalyst precursors than [Pt(PPh3)4] for the
diboration of alkynes and that B2(cat)2 reacts faster than
B2(pin)2, which in turn is much faster than B2(4-But-
cat)2. Initial results indicate that decomposition of the
Pt(II) bis(boryl) compounds gives rise to the boron-
containing products B2(cat)3 and B2(pin)3. The resulting
[(PPh3)2Pt] species may react with solvent in the
absence of diboron reagent or alkyne, or with B2(cat)3,
to produce metal hydride products incapable of cata-
lyzing the desired reactions. Furthermore, the stability
of [(PPh3)nPt(η-alkyne)] compounds and subsequent
competing reactions leads to reduced rates for the
diboration of π-acceptor-substituted alkynylarene de-
rivatives. An important step in the catalyzed diboration
of alkynes appears to be the dissociation of phosphine
from the (PPh3)2Pt complexes, giving rise to a mono-
(phosphine)Pt intermediate which serves as the active
catalyst in these systems. We have also found that
diynes can be either diborated or tetraborated in a
controlled fashion using these systems and that novel
products, including vinyl-tris(boronate esters), are ob-
tained via tCsSi bond cleavage with Me3SiCtCSiMe3.
Further work is in progress to develop even more active
catalyst precursors involving Pt and Ni mono(phos-
phine) analogues. Preliminary results employing (η-
COD)2Pt and 1 equiv of P(o-tolyl)3 demonstrate that this
system provides significant activity for addition of B2-
(pin)2 (1c) to 4-MeOPhCtCPh-4-OMe (8g) at room
temperature in toluene.
Iverson and Smith7b recently reported that (PPh3)2-
Pt(Bpin)2 (3c) is prone to reductive elimination in the
presence of a variety of substrates, including 1a , and
that in the presence of alkyne an equilibrium exists
between 3c and a (PPh3)2Pt(η-alkyne) complex plus B2-
(27) Waltz, K. M.; He, X.; Muhoro, C.; Hartwig, J . F. J . Am. Chem.
Soc. 1995, 117, 11357.
(28) The inability to isolate dihydride compounds of (PPh3)2Pt has
been noted: Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Chem. Commun.
1976, 365.

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5149
Cortho of P(C6H5)3), 129.4 (m, 12C, Cmeta of P(C6H5)3), 119.9 (s,
4C, C4 and C5 of 1,2-O2C6H4), 111.0 (s, 4C, C3 and C6 of 1,2-
O2C6H4) + toluene of solvation. These values are similar, but
not identical, with those reported in ref 7a. Those authors
have not reported 13C NMR data, nor did they observe the
broad 11B resonance for 3a in the initial study. Anal. Calcd
for C48H38B2O4P2Pt‚C7H8: C, 62.94; H, 4.42. Found: C, 62.61;
H, 4.71.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were performed
under a dry nitrogen atmosphere using glovebox techniques.
Reaction solvents were dried using the appropriate drying
agents and distilled under an N2 atmosphere: toluene, diethyl
ether, and THF from Na/benzophenone, hexanes from Na
metal, and DMF from CaH2. NMR solvents were distilled from
CaH2 (CDCl3) or Na metal (C6D6) following three freeze/pump/
thaw cycles. Alkynes were prepared by reported routes29 or
obtained from commercial sources. Phenylacetylene and 1-oc-
tyne were degassed via three freeze/pump/thaw cycles and
vacuum-distilled prior to use. The synthesis of compounds
1a -c has been discussed previously.5,30 All starting reagents
were checked for purity using GC/MS and/or NMR prior to
use. Melting point determinations were made using a Mel-
Temp II (Laboratory Devices) apparatus equipped with a Fluke
51 thermocouple (J ohn Fluke Mfg. Co.) with samples sealed
in glass capillary tubes using wax.
cis-[(P P h 3)2P t(B(1,2-O2-4-Bu tC6H3))2] (3b). This com-
pound was prepared similarly to compound 3a : yield ) 88%;
mp 184.3-185.6 °C (dec, 137 °C); 31P{1H} NMR δ 29.0 (br, J Pt-P
) 1621 Hz); 11B{1H} δ 50.1 (br); 1H NMR δ 7.36 (m, 12H,
P(C6H5)3), 7.05 (m, 18H, P(C6H5)3), 6.81 (t, J ) 1.1 Hz, 2H, H3
of (1,2-O2-4-ButC6H3)), 6.68 (2 coincidently overlapped doublets,
both with J ) 1.1 Hz, 4H, H6 and H5 of (1,2-O2-4-ButC6H3)),
3
1.20 (s, 18H, C(CH3)3); 13C{1H} NMR δ 150.5 (s, 2C, J Pt-C
)
35 Hz, C2 of (1,2-O2-4-ButC6H3)), 148.4 (s, 2C, J Pt-C ) 35 Hz,
3
C1 of (1,2-O2-4-ButC6H3)), 143.4 (s, 2C, C4 of (1,2-O2-4-
ButC6H3)), 135.5 (d, 6C, J P-C) 44 Hz, J Pt-C ) 20 Hz, Cipso of
P(C6H5)3), 134.0 (m, 12C, Cortho of P(C6H5)), 129.4 (s, 6C, Cpara
of P(C6H5)), 127.7 (m, 12C, Cmeta of P(C6H5)), 116.3 (s, 2C, C5
of (1,2-O2-4-ButC6H3)), 109.8 (s, 2C, C3 of (1,2-O2-4-ButC6H3)),
108.6 (s, 2C, C6 of (1,2-O2-4-ButC6H3)), 34.3 (s, 2C, C(CH3)3),
31.7 (s, 2C, C(CH3)3). Anal. Calcd for C56H54B2O4P2Pt: C,
62.88; H, 5.09. Found: C, 62.95; H, 5.16.
1
2
Nuclear magnetic resonance experiments were performed
on Bruker AC200 or AMX 500 spectrometers at the following
frequencies, unless otherwise stated: 1H, 200 and 500 MHz;
13C{1H}, 50 and 125 MHz; 11B{1H}, 64 MHz; 31P{1H}, 81 MHz.
The 1H chemical shifts were referenced to the internal
standard tetramethylsilane (TMS), and 13C chemical shifts
were referenced to the solvent resonances as an internal
standard. The 11B and 31P chemical shifts are referenced to
the external standards F3B‚OEt2 and 85% H3PO4, respectively.
The 11B NMR spectra were obtained using a background
subtraction routine to remove resonances due to borosilicate
glass in the NMR probe and NMR tube. This was ac-
complished by recording the spectrum of an NMR tube
containing the same height of pure solvent with collection
parameters identical with those for the sample and subtracting
this background FID from that of the sample. Spectra were
recorded in CDCl3 unless otherwise stated. Elemental analy-
ses were obtained from M-H-W Laboratories, Phoenix, AZ.
cis-[(P P h 3)2P t(B(OC(CH3)2C(CH3)2O))2] (3c). The com-
pound [(PPh3)2Pt(η-C2H4)] (4; 212 mg, 0.284 mmol) and B2-
(pin)2 (1c; 72 mg, 0.284 mmol) were placed in a scintillation
vial, and CDCl3 (1 mL) was added. The solution was stirred
at ambient temperature, and the slow evolution of ethylene
gas was apparent. The reaction mixture was stirred overnight,
resulting in a red solution which was analyzed by NMR
spectroscopy: 31P{1H} NMR δ 28.5 (br, J Pt-P ) 1504 Hz, 3c),
26.5 (sh, J Pt-P ) 3189 Hz); 11B{1H} NMR δ ca. 50 (vbr, 3c),
30.1 (1c), 21.4 (7).
Syn th esis of cis-[(P P )P t(Bca t)2] Com p ou n d s (P P
)
d p p e, d p p b). cis-[(P h 2P CH2CH2P P h 2)P t(B(1,2-O2C6H4))2]
(5a ). Compound 3a (250 mg, 0.261 mmol) was dissolved in
toluene (5 mL), and dppe (104 mg, 0.261 mmol) was added as
a toluene solution (3 mL) via pipet. The solution was stirred
overnight, and a white precipitate formed, which was collected
by filtration and dried in vacuo: yield 165 mg (76%); mp
225.0-226.8 °C (dec, 170 °C); 31P{1H} NMR (C6D6/THF) δ 57.8
GC/MS analyses were performed on a Hewlett-Packard 5890
Series II/5971A MSD instrument equipped with an HP 7673A
autosampler and a fused silica column (30 m × 0.25 mm, cross-
linked 5% phenylmethyl silicone). The following operating
conditions were used: injector, 260 °C; transfer line, 280 °C;
oven temperature was ramped from 70 to 260 °C at the rate
of 20 °C/min. UHP grade helium was used as the carrier gas.
The parent ions [M + H]+ for compounds 15a ,b were
observed by injecting a 10 µL sample of the crude product into
a VG/Fisons (Manchester, UK) Quattro II triple quadropole
mass spectrometer fitted with an electrospray source. A 50/
50 mixture of H2O and CH3CN was used as a carrier solution
at a rate of 10 mL/min, and samples were introduced directly
into the electrospray source.
1
(J Pt-P ) 1454 Hz); 11B{1H} NMR (C6D6/THF) δ 48.9 (br); H
NMR δ 7.74 (m, 8H, P(C6H5)3), 7.34 (m, 12H, P(C6H5)3), 7.06
(m, 4H, 1,2-O2C6H4), 6.84 (m, 4H, 1,2-O2C6H4), 2.38 (dm, J )
17.5 Hz, 4H, PCH2); 13C{1H} NMR δ 150.0 (4C, C1 and C2 of
(1,2-O2C6H4)), 134.8 (br, s, 4C, Cipso of P(C6H5)3), 133.3 (m, 8C,
Cortho of P(C6H5)3), 130.6 (4C, Cpara of P(C6H5)3), 128.6 (m, 8C,
Cmeta of P(C6H5)3), 120.5 (4C, C4 and C5 of (1,2-O2C6H4)), 111.3
(4C, C3 and C6 of (1,2-O2C6H4)), 29.3 (m, 2C, CH2). Anal. Calcd
for C38H32B2O4P2Pt: C, 54.90; H, 3.88. Found: C, 54.54; H,
3.66.
Syn th esis of cis-[(P P h 3)2P t(bor yl)2] Com p ou n d s. cis-
[(P P h 3)2P t (B(1,2-O2C6H 4))2]‚C7H 8 (3a ). The compound
[(PPh3)2Pt(η-C2H4)]9 (4; 1.000 g, 1.337 mmol) was dissolved in
toluene (5 mL), and solid B2(cat)2 (1a ; 318 mg, 1.337 mmol)
was added portionwise with a spatula. The solution was
stirred at ambient temperature, and the evolution of ethylene
gas was apparent. A white precipitate began to form im-
mediately, which was collected by filtration after 30 min,
washed with cold toluene (5 mL) and dried in vacuo: yield
1.236 g (88%); mp 170.2-171.2 °C (dec, 111 °C); 31P{1H} NMR
δ 28.7 (br, J Pt-P ) 1639 Hz); 11B{1H} NMR δ 47.0 (br); 1H NMR
δ 7.36 (m, 12H, P(C6H5)3), 7.08 (m, 18H, P(C6H5)3), 6.77 (m,
4H, 1,2-O2C6H4), 6.68 (m, 4H, 1,2-O2C6H4) + toluene of
cis-[(P h 2P (CH2)4P P h 2)P t(B(1,2-O2C6H4))2] (5b). This com-
pound was prepared similarly to compound 5a : yield 174 mg
(77%); mp 209.3-210.3 °C (dec, 165 °C); 31P{1H} NMR (C6D6/
THF) δ 21.6 (J Pt-P ) 1589 Hz); 11B{1H} NMR (C6D6/THF) δ
48.9 (br); 1H NMR δ 7.50 (m, 8H, P(C6H5)3), 7.21 (m, 12H,
P(C6H5)3), 6.83 (m, 4H, 1,2-O2C6H4), 6.72 (m, 4H, 1,2-O2C6H4),
2.68 (br, s, 4H, P-CH2), 1.84 (br, d, J ) 20 Hz, 4H, P-CH2CH2);
13C{1H} NMR δ 149.9 (s, 4C, 3J Pt-C ) 34 Hz, C1 and C2 of (1,2-
O2C6H4)), 135.9 (d, 4C, 1J P-C ) 47 Hz, Cipso of P(C6H5)3), 132.7
(m, 8C, Cortho of P(C6H5)3), 129.7 (s, 4C, Cpara of P(C6H5)3), 128.1
(m, 8C, Cmeta of P(C6H5)3), 120.1 (s, 4C, C4 and C5 of (1,2-
O2C6H4)), 111.0 (s, 4C, C3 and C6 of (1,2-O2C6H4)), 28.0 (m,
2C, P-CH2), 23.9 (m, 2C, PCH2CH2). Anal. Calcd for
3
solvation; 13C NMR δ 149.7 (s, 4C, J Pt-C ) 34 Hz, C1 and C2
C
40H36B2O4P2Pt: C, 55.91; H, 4.22. Found: C, 55.22; H, 4.03.
of 1,2-O2C6H4)), 134.9 (s, 6C, Cipso of P(C6H5)3), 134.0 (m, 12C,
Syn th esis of B2(OC(CH3)2C(CH3)2O)3 (7). A 1 M solution
of BH3 in THF (2.8 mL, 2.8 mmol) was added dropwise to a
THF solution (15 mL) of HOC(CH3)2C(CH3)2OH (500 mg, 4.23
mmol), and the evolution of gas was apparent. The solution
was stirred for 14 h and reduced in vacuo. The residue was
dissolved in toluene and filtered through Celite. The filtrate
(29) (a) Nguyen, P.; Todd, S.; Van den Biggelaar, D.; Taylor, N. J .;
Marder, T. B.; Wittmann, F.; Friend, R. H. Synlett 1994, 299. (b)
Nguyen, P.; Yuan, Z.; Agocs, L.; Lesley, G.; Marder, T. B. Inorg. Chim.
Acta 1994, 220, 289.
(30) No¨th, H. Z. Naturforsch. 1984, 39B, 1463.

5150 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
was reduced in vacuo and redissolved in CDCl3 for analysis:
1H NMR δ 1.23 (s, 24H), 1.37 (s, 12H); 13C{1H} NMR δ 81.9
(4C), 79.5 (2C), 24.5 (8C), 22.7 (4C); 11B NMR δ 21.9.
123.2 (2C, C4 and C5 of (1,2-O2C6H4)), 123.0 (2C, C4 and C5 of
(1,2-O2C6H4)), 118.7 (1C, CtN) , 112.8 (2C, C3 and C6 of (1,2-
O2C6H4)), 112.6 (2C, C3 and C6 of (1,2-O2C6H4)), 112.3 (1C, C4
of NCC6H4); 11B{1H} NMR (64 MHz) δ 31.5 (br, overlapped,
2B).
Ca ta lytic Syn th esis of Bis(bor on a te ester s). In
a
typical catalytic reaction, in an N2 filled glovebox, a thick-
walled tube capped with a Youngs stopcock was charged with
alkyne 8a -h or diyne 9a ,b (1.9 × 10-4 mol), diboron reagent
1a ,c (1.9 × 10-4 mol, or 3.8 × 10-4 mol for 9a ,b), catalyst 4 or
3b (ca. 5.7 × 10-6 mol, 3 mol %), and toluene (5 mL). The
tube was sealed and heated to 80 °C, and aliquots (1 µL) were
removed hourly to monitor the disappearance of alkyne via
GC/MS. Upon completion, the toluene was removed in vacuo,
and the crude product was analyzed by GC/MS and 1H, 11B-
{1H}, and 13C{1H} NMR spectroscopy (CDCl3). All compounds
containing the Bpin functional groups were stable under the
GC/MS conditions, whereas those containing Bcat functional
groups could not be observed in many cases due to decomposi-
tion in the injector or on the column. Observed isotope
distributions for parent ions showed excellent agreement with
calculated ones. For the GC/MS analysis of compounds 11h ,
16, and 17-21 the relative intensities of the fragments with
respect to the largest peak in the spectra are included. The
values reported in amu for the fragments formed represent in
each case the peak with the largest contribution to the
surrounding isotopic pattern. In some instances the parent
ions were not observed; however, in all of these cases the
observed isotope distributions were in agreement with calcu-
lated ones for the parent ion minus one methyl group.
(E)-C6H13C(B(1,2-O2C6H4))dCH(B(1,2-O2C6H4)) (10a ): 1H
NMR (500 MHz) δ 7.18 (m, 2H, (1,2-O2C6H4)), 7.05 (m, 4H,
(1,2-O2C6H4)), 6.98 (m, 2H, (1,2-O2C6H4)), 6.51 (s, 1H, CdCH),
2.56 (t, J ) 6.9 Hz, 2H, dCCH2), 1.58 (m, 2H, dCCH2CH2),
1.29 (m, 6H, CH3(CH2)3), 0.89 (t, 3H, CH3); 13C{1H} NMR (125
MHz) δ 156.7 (br, 1C, BsC), 148.14 (2C, C1 and C2 of (1,2-
O2C6H4)), 148.10 (2C, C1 and C2 of (1,2-O2C6H4)), 129.7 (br,
1C, BsC), 122.7 (2C, C4 and C5 of (1,2-O2C6H4)), 122.5 (2C, C4
and C5 of (1,2-O2C6H4)), 112.4 (2C, C3 and C6 of (1,2-O2C6H4)),
112.3 (2C, C3 and C6 of (1,2-O2C6H4)), 39.8 (1C, CdC-CH2), 31.6
(1C, dCCH2CH2), 28.9 (1C, dCCH2CH2CH2), 28.7 (1C, CH3-
CH2CH2), 22.6 (1C, CH3CH2CH2), 14.0 (1C, CH3CH2CH2); 11B-
{1H} NMR (64 MHz), δ 31.7 (br, overlapped, 2B).
(E)-C6H5C(B(1,2-O2C6H4))dCH(B(1,2-O2C6H4)) (10b): 1H
NMR (200 MHz) δ 7.54 (m, 2H, C6H5), 7.30 (m, 3H, C6H5), 7.25
(m, 2H, (1,2-O2C6H4)), 7.10 (m, 2H, (1,2-O2C6H4)), 7.01 (s, 4H,
(1,2-O2C6H4)), 6.98 (s, 1H, CdCH); 13C{1H} NMR (50 MHz) δ
154.5 (br, 1C, BsC), 148.2 (2C, C1 and C2 of (1,2-O2C6H4)),
147.9 (2C, C1 and C2 of (1,2-O2C6H4)), 140.5 (1C, C6H5), 128.9
(1C, C6H5), 128.7 (2C, C6H5), 126.7 (2C, C6H5), 122.8 (2C, C4
and C5 of (1,2-O2C6H4)), 122.6 (2C, C4 and C5 of (1,2-O2C6H4)),
112.6 (2C, C3 and C6 of (1,2-O2C6H4)), 112.3 (2C, C3 and C6 of
(1,2-O2C6H4)) (one CsB resonance not observed); 11B{1H} NMR
(64 MHz) δ 31.4 (br, overlapped, 2B).
(E )-(4-M e O -C 6 H 4 )C (B (1,2-O 2 C 6 H 4 ))dC H (B (1,2-O 2 -
C6H4)) (10c): mp 108.7-109.8 °C; 1H NMR (200 MHz) δ 7.52
(d, J ) 8.8 Hz, 2H, MeOC6H4), 7.30 (m, 2H, (1,2-O2C6H4)), 7.16
(m, 2H, (1,2-O2C6H4)), 6.98 (s, 4H, (1,2-O2C6H4)), 6.90 (d, J )
8.8 Hz, 2H, MeOC6H4), 6.87 (s, 1H, CdCH), 3.81 (s, 3H,
MeOC6H4); 13C{1H} NMR (50 MHz) δ 160.5 (1C, C4 of
MeOC6H4), 154.0 (br, BsC), 148.3 (2C, C1 and C2 of (1,2-
O2C6H4)), 148.0 (2C, C1 and C2 of (1,2-O2C6H4)), 133.1 (1C, C1
of MeOC6H4), 128.4 (2C, C2 and C6 of MeOC6H4), 124.0 (br,
BsC), 122.9 (2C, C4 and C5 of (1,2-O2C6H4)), 122.6 (2C, C4 and
C5 of (1,2-O2C6H4)), 114.2 (2C, C3 and C5 of MeOC6H4), 112.7
(2C, C3 and C6 of (1,2-O2C6H4)), 112.3 (2C, C3 and C6 of (1,2-
O2C6H4)), 55.3 (OCH3); 11B{1H} NMR (64 MHz) δ 32.0 (br,
overlapped, 2B).
(Z)-(C6H 5)C(B(1,2-O2C6H 4))dC(C6H 5)(B(1,2-O2C6H 4))
(10e): mp 161.2-162.4 °C; 1H NMR (200 MHz) δ 7.18 (m, 10H,
C6H5), 7.05 (m, 4H, (1,2-O2C6H4)), 7.00 (m, 4H, (1,2-O2C6H4));
13C{1H} NMR (50 MHz) δ 148.0 (4C, C1 and C2 of (1,2-O2C6H4)),
139.1 (2C, CdCC), 129.2 (4C, C6H5), 128.2 (4C, C6H5), 127.1
(2C, C6H5), 122.8 (4C, C4 and C5 of (1,2-O2C6H4)), 112.5 (4C,
C3 and C6 of (1,2-O2C6H4)) (CsB resonances too broad to
observe); 11B{1H} NMR (64 MHz) δ 31.8. Anal. Calcd for
C
26H18B2O4: C, 75.06; H, 4.36. Found: C, 75.21; H, 4.50.
(Z)-(4-Me-C6H4)C(B(1,2-O2C6H4))dC(4-Me-C6H4)(B(1,2-
O2C6H4)) (10f): mp 197.8-198.6 °C; 1H NMR (C6D6, 250 MHz)
δ 7.22 (d, J ) 8.0 Hz, 4H, MeC6H4), 6.89 (m, 4H, (1,2-O2C6H4)),
δ 6.83 (d, J ) 8.0 Hz, 4H, MeC6H4), 6.73 (m, 4H, (1,2-O2C6H4)),
1.98 (s, 6H, MeC6H4); 13C{1H} NMR (50 MHz) δ 148.2 (4C, C1
and C2 of (1,2-O2C6H4)), 136.9 (2C, C4 of 4-MeC6H4), 136.3 (2C,
C1 of 4-MeC6H4), 129.3 (4C, C2 and C6 of MeC6H4), 129.0 (4C,
C3 and C5 of MeC6H4), 122.7 (4C, C4 and C5 of (1,2-O2C6H4)),
112.5 (4C, C3 and C6 of (1,2-O2C6H4)), 21.2 (2C, CH3C6H4) (CsB
resonances too broad to observe); 11B{1H} NMR (64 MHz) δ
31.2.
(Z)-(4-MeO-C6H4)C(B(1,2-O2C6H4))dC(4-MeO-C6H4)(B(1,2-
O2C6H4)) (10g): 1H NMR (200 MHz) δ 7.13 (d, J ) 8.6 Hz,
4H, MeOC6H4), 7.03 (m, 8H, (1,2-O2C6H4)), 6.74 (d, J ) 8.6
Hz, 4H, MeOC6H4), 3.70 (s, 6H, MeOC6H4); 13C{1H} NMR (50
MHz) δ 158.7 (2C, C4 of MeOC6H4), 148.1 (4C, C1 and C2 of
(1,2-O2C6H4)), 144.3 (br, 2C, BsC), 131.6 (2C, C1 of MeOC6H4),
130.7 (4C, C2 and C6 of MeOC6H4), 122.7 (4C, C4 and C5 of
(1,2-O2C6H4)), 113.7 (4C, C3 and C5 of MeOC6H4), 112.4 (4C,
C3 and C6 of (1,2-O2C6H4)), 55.0 (2C, CH3O); 11B{1H} NMR (64
MHz) δ 31.8.
(E)-C6H13C(B(OC(CH3)2C(CH3)2O))dCH(B(OC(CH3)2C-
1
(CH3)2O)) (11a ): H NMR (200 MHz) δ 5.85 (s, 1H, CdCH),
2.23 (t, J ) 6.2 Hz, 2H, CdCCH2), 1.40-1.20 (m, 8H, CdCCH2-
(CH2)4), 1.33 (s, 12H, (OC(CH3)2C(CH3)2O)), 1.23 (s, 12H, (OC-
(CH3)2C(CH3)2O)), 0.88 (t, J ) 6.7 Hz, 3H, CH3); 13C{1H} NMR
(50 MHz), δ 83.2 (2C, (OC(CH3)2C(CH3)2O)), 82.8 (2C, (OC-
(CH3)2C(CH3)2O)), 39.6 (CdCCH2), 31.4 (CdCCH2CH2), 28.8
(CdCCH2CH2CH2), 28.3 (CH3CH2CH2), 24.6 (8C, overlapped,
(OC(CH3)2C(CH3)2O)), 22.7 (CH3CH2), 13.7 (CH3) (CsB reso-
nances too broad to observe); 11B{1H} NMR (64 MHz) δ 30.7
(br, overlapped, 2B); MS (EI) m/ z 364 amu (M+ for
12
C
1H3811B216O4).
20
(E)-C6H 5C(B(OC(CH 3)2C(CH 3)2O))dCH (B(OC(CH 3)2C-
1
(CH3)2O)) (11b): H NMR (250 MHz) δ 7.43 (m, 2H, C6H5),
7.28 (m, 3H, C6H5), 6.29 (s, 1H, CdCH), 1.37 (s, 12H, (OC-
(CH3)2C(CH3)2O)), 1.30 (s, 12H, (OC(CH3)2C(CH3)2O)); 13C{1H}
NMR (50 MHz) δ 142.8 (1C, C6H5), 128.1 (2C, C6H5), 127.4
(1C, C6H5), 126.3 (2C, C6H5), 83.9 (2C, (OC(CH3)2C(CH3)2O)),
83.2 (2C, (OC(CH3)2C(CH3)2O)), 24.9 (4C, (OC(CH3)2C(CH3)2O)),
24.7 (4C, (OC(CH3)2C(CH3)2O)) (CsB resonances too broad to
observe); 11B{1H} NMR (64 MHz) δ 30.2 (br, overlapped, 2B);
MS (EI) m/ z 356 amu (M+ for
C
1H3011B216O4).
12
20
(E)-(4-MeO-C6H4)C(B(OC(CH3)2C(CH3)2O))dCH(B(OC-
1
(CH3)2C(CH3)2O)) (11c): H NMR (250 MHz) δ 7.39 (d, J )
8.6 Hz, 2H, MeOC6H4), 6.84 (d, J ) 8.6 Hz, 2H, MeOC6H4),
6.21 (s, 1H, CdCH), 3.79 (s, 3H, CH3O), 1.33 (s, 12H, (OC-
(CH3)2C(CH3)2O)), 1.30 (s, 12H, (OC(CH3)2C(CH3)2O)); 13C{1H}
NMR (50 MHz) δ 159.3 (1C, C4 of MeOC6H4), 135.4 (1C, C1 of
MeOC6H4), 127.7 (2C, C2 and C6 of MeOC6H4), 113.6 (2C, C3
and C5 of MeOC6H4), 83.9 (2C, (OC(CH3)2C(CH3)2O)), 83.3 (2C,
(OC(CH3)2C(CH3)2O)), 55.0 (CH3O), 25.0 (4C, (OC(CH3)2C-
(CH3)2O)), 24.8 (4C, (OC(CH3)2C(CH3)2O)) (CsB resonances too
(E)-(4-NC-C6H 4)C(B(1,2-O2C6H 4))dCH (B(1,2-O2C6H 4))
(10d ): 1H NMR (200 MHz) δ 7.70 (s, broad, 4H, NCC6H4), 7.26
(m, 2H, (1,2-O2C6H4)), 7.17 (m, 2H, (1,2-O2C6H4)), 7.08 (s,
broad, 4H, (1,2-O2C6H4)), 7.05 (s, 1H, CdCH); 13C{1H} NMR
(50 MHz) δ 148.0 (2C, C1 and C2 of (1,2-O2C6H4)), 147.9 (2C,
C1 and C2 of (1,2-O2C6H4)), 145.3 (1C, C1 of NCC6H4), 132.6
(2C, C3 and C5 of NCC6H4), 127.7 (2C, C2 and C6 of NCC6H4),
broad to observe); 11B{1H} NMR (64 MHz) δ 30.2 (br, over-
lapped, 2B); MS (EI) m/ z 386 amu (M+ for
C
1H3211B216O5).
12
21
(E)-(4-NC-C6H 4)C(B(OC(CH 3)2C(CH 3)2O))dCH (B(OC-
1
(CH3)2C(CH3)2O)) (11d ): H NMR (200 MHz) δ 7.59 (d, J )
8.3 Hz, 2H, NCC6H4), 7.51 (d, J ) 8.3 Hz, 2H, NCC6H4), 6.37
(s, 1H, CdCH), 1.37 (s, 12H, (OC(CH3)2C(CH3)2O)), 1.32 (s,

Platinum(II)-Bis(boryl) Catalyst Precursors
Organometallics, Vol. 15, No. 24, 1996 5151
12H, (OC(CH3)2C(CH3)2O)); 13C{1H} NMR (50 MHz) δ 147.7
(1C, C1 of NCC6H4), 132.1 (2C, C3 and C5 of NCC6H4), 127.2
(2C, C2 and C6 of NCC6H4), 119.0 (1C, CtN), 110.0 (1C, C4 of
NCC6H4), 84.4 (2C, (OC(CH3)2C(CH3)2O)), 83.9 (2C, (OC-
(CH3)2C(CH3)2O)), 24.8 (4C, (OC(CH3)2C(CH3)2O)), 24.5 (4C,
(OC(CH3)2C(CH3)2O)) (CsB resonances too broad to observe);
(1,2-O2C6H4)), 6.65 (d, J ) 8.7 Hz, 4H, MeOC6H4), 3.61 (s, 6H,
CH3O); 13C{1H} NMR (50 MHz) δ 159.5 (2C, C4 of MeOC6H4),
148.1 (8C, C1 and C2 of (1,2-O2C6H4)), 132.7 (2C, C1 of
MeOC6H4), 130.9 (4C, C2 and C6 of MeOC6H4), 122.7 (4C, C4
and C5 of (1,2-O2C6H4)), 122.2 (4C, C4 and C5 of (1,2-O2C6H4)),
113.9 (4C, C3 and C5 of MeOC6H4), 112.5 (4C, C3 and C6 of
(1,2-O2C6H4)), 111.9 (4C, C3 and C6 of (1,2-O2C6H4)), 55.1 (2C,
CH3O) (CsB resonances too broad to observe); 11B{1H} NMR
(64 MHz) δ 30.7 (br, overlapped, 4B). Anal. Calcd for
11B{1H} NMR (64 MHz) δ 30.9 (br, overlapped, 2B); MS (EI)
m/ z 381 amu (M+ for
C
1H2911B214N16O4).
12
21
(Z)-(C6H5)C(B(OC(CH3)2C(CH3)2O))dC(C6H5)(B(OC(C-
H3)2C(CH3)2O)) (11e): 1H NMR (200 MHz) δ 7.05 (m, 6H,
C6H5), 6.94 (d, J ) 6.8 Hz, 4H, C6H5), 1.32 (s, 24H, (OC(CH3)2C-
(CH3)2O)); 13C{1H} NMR (50 MHz), 141.3 (2C, CdCC), 129.3
(4C, C6H5), 127.4 (2C, C6H5), 125.8 (4C, C6H5), 84.1 (4C,
(OC(CH3)2C(CH3)2O)), 24.9 (8C, (OC(CH3)2C(CH3)2O) (CsB
C
42H30B4O10: C, 68.36; H, 4.10. Found: C, 68.56; H, 4.22.
(Z,Z)-(4-MeO-C6H4)C(B(OC(CH3)2C(CH3)2O))dC(B(OC-
(CH 3)2C(CH 3)2O))C(B(OC(CH 3)2C(CH 3)2O))dC(4-Me O-
1
C6H4)(B(OC(CH3)2C(CH3)2O)) (15a ): H NMR (200 MHz) δ
7.19 (d, J ) 8.7 Hz, 4H, MeOC6H4), 6.73 (d, J ) 8.7 Hz, 4H,
MeOC6H4), 3.73 (s, 6H, CH3O), 1.29 (s, 12H, (OC(CH3)2C-
(CH3)2O)), 1.25 (s, 12H, (OC(CH3)2C(CH3)2O)), 1.00 (s, 12H,
(OC(CH3)2C(CH3)2O)), 0.95 (s, 12H, (OC(CH3)2C(CH3)2O)); 13C-
{1H} NMR (50 MHz) δ 157.9 (2C, C4 of MeOC6H4), 147.1
(BsC), 142.2 (BsC), 137.7 (2C, C1 of MeOC6H4), 130.0 (4C,
C2 and C6 of MeOC6H4), 112.9 (4C, C3 and C5 of MeOC6H4),
83.0 (4C, (OC(CH3)2C(CH3)2O)), 82.9 (4C, (OC(CH3)2C(CH3)2O)),
55.1 (CH3O), 25.2 (4C, (OC(CH3)2C(CH3)2O)), 24.8 (4C, (OC-
(CH3)2C(CH3)2O)), 24.5 (4C, (OC(CH3)2C(CH3)2O)), 24.3 (4C,
(OC(CH3)2C(CH3)2O)); 11B{1H} NMR (64 MHz) δ 30.0 (br,
overlapped, 4B); MS (electrospray) 771 amu (M + H+ for
resonances too broad to observe); 11B{1H} NMR (64 MHz) δ
30.6; MS (EI) m/ z 432 amu (M+ for
C
1H3411B216O4).
12
26
(Z)-(4-Me-C6H4)C(B(OC(CH3)2C(CH3)2O))dC(4-Me-C6H4)-
(B(OC(CH3)2 C(CH3)2O)) (11f): 1H NMR (200 MHz) δ 6.86
(m, 8H overlapping, MeC6H4), 2.22 (s, 6H, CH3C6H4), 1.31 (s,
24H, (OC(CH3)2C(CH3)2O)); 13C{1H} NMR (50 MHz) δ 138.3
(2C, C4 of MeC6H4), 135.1 (2C, C1 of MeC6H4), 129.2 (4C, C2
and C6 of MeC6H4), 128.2 (4C, C3 and C5 of MeC6H4), 83.9 (4C,
(OC(CH3)2C(CH3)2O)), 24.9 (8C, (OC(CH3)2C(CH3)2O)), 54.9
(2C, CH3C6H4); 11B{1H} NMR (64 MHz) δ 31.2; MS (EI) m/ z
460 amu (M+ for
C
1H3811B216O4).
12
28
12
16
C
1H6211B4
O ).
10
42
(Z)-(4-MeO-C6H 4)C(B(OC(CH 3)2C(CH 3)2O))dC(4-MeO-
C6H4)(B(OC(CH3)2 C(CH3)2O)) (11g): mp 176.6-177.3 °C; 1H
NMR (200 MHz) δ 6.89 (d, J ) 8.8 Hz, 4H, MeOC6H4), 6.62
(d, J ) 8.8 Hz, 4H, MeOC6H4), 3.68 (s, 6H, CH3O), 1.32 (s,
24H, (OC(CH3)2C(CH3)2O)); 13C{1H} NMR (50 MHz) 157.6 (2C,
C4 of MeOC6H4), 144.9 (br, 2C, BsC), 133.8 (2C, C1 of
MeOC6H4), 130.6 (4C, C2 and C6 of MeOC6H4), 113.4 (4C, C3
and C5 of MeOC6H4), 83.9 (4C, (OC(CH3)2C(CH3)2O)), 54.9 (2C,
(Z,Z)-(Me3Si)C(B(OC(CH3)2C(CH3)2O))dC(B(OC(CH3)2C-
(C H 3)2O ))C (B (O C (C H 3)2C (C H 3)2O ))dC (S iMe 3)(B (O C -
(CH3)2C(CH3)2O)) (15b): MS (electrospray) 703 amu (M + H+
12
for
C
1H6611B416O828Si2).
34
C6H5CtCC(H)dCH(C6H5) (16): configuration unknown;
MS (EI) m/ z (relative intensity) 204 (100) amu (M+ for
12
C
1H12), 189 (6.4), 176 (5.5), 165 (4.5), 150 (3.3), 139 (2.0),
16
CH3O), 24.9 (8C, (OC(CH3)2C(CH3)2O)); 11B{1H} NMR (64
126 (9.2), 115 (1.2), 101 (15.4), 89 (6.3), 76 (6.9), 63 (4.4), 51
(6.9).
MHz) δ 30.5; MS (EI) m/ z 492 amu (M+ for
C
1H3811B216O6).
12
28
Anal. Calcd for C28H38B2O6: C, 68.32; H, 7.78. Found: C,
68.31; H, 7.86.
(Me3Si)C(B(OC(CH 3)2C(CH 3)2O))dC(SiMe3)(B(OC(C-
C 6 H 5 C (B (O C (C H 3 )2 C (C H 3 )2 O ))dC (B (O C (C H 3 )2 C -
(CH3)2O))C(H)dCH(C6H5) (17): configuration unknown; MS
(EI) m/ z (relative intensity) 458 (5.6) amu (M+ for
12
C
1H3611B216O4), 400 (2.6), 358 (5.6), 330 (20.6), 315 (3.3), 301
H3)2C(CH3)2O)) (11h ): MS (EI) m/ z (relative intensity) 424
28
amu (M+ for
C
1H4211B216O428Si2, 1.6), 409 (5.1), 225 (1.9),
12
(9.5), 275 (25.8), 257 (31.7), 241 (4.8), 231 (39.9), 213 (49.8),
204 (100), 187 (6.0), 167 (3.3), 155 (9.8), 129 (11.6), 115 (4.6),
101 (12.1), 84 (57.9), 69 (31.0), 55 (24.7).
20
209 (1.5), 167 (3.1), 155 (3.3), 143 (2.4), 135 (1.0), 125 (2.5),
109 (1.8), 101 (2.5), 84 (100), 75 (3.6), 69 (14.4), 55 (7.2).
(Z )-(4-M e O -C 6 H 4 )C (B (O C (C H 3 )2 C (C H 3 )2 O ))dC (B -
(OC(CH3)2C(CH3)2O))CtC(4-MeO-C6H4) (13a ): 1H NMR
(200 MHz) δ 7.58 (d, J ) 8.7 Hz, 2H, tCC6H4), 7.23 (d, J )
8.7 Hz, 2H, dCC6H4), 6.88 (d, J ) 8.7 Hz, 2H, tCC6H4), 6.76
(d, J ) 8.7 Hz, 2H, dCC6H4), 3.80 (s, 3H, CH3O), 3.75 (s, 3H,
CH3O), 1.37 (s, 12H, (OC(CH3)2C(CH3)2O)), 1.31 (s, 12H, (OC-
(CH3)2C(CH3)2O)); 13C{1H} NMR (50 MHz), δ 159.2 (1C, C4 of
MeOC6H4), 158.7 (1C, C4 of MeOC6H4), 133.7 (1C, C1 of
MeOC6H4), 133.0 (2C, C2 and C6 of MeOC6H4), 130.1 (2C, C2
and C6 of MeOC6H4), 116.5 (1C, C1 of MeOC6H4), 113.6 (2C,
C3 and C5 of MeOC6H4), 112.8 (2C, C3 and C5 of MeOC6H4),
97.1 (CtC), 89.6 (CtC), 84.1 (2C, (OC(CH3)2C(CH3)2O)), 84.0
(2C, (OC(CH3)2C(CH3)2O)), 55.1 (CH3O), 55.0 (CH3O), 24.8 (4C,
(OC(CH3)2C(CH3)2O)), 24.7 (4C, (OC(CH3)2C(CH3)2O)) (CsB
resonances too broad to observe); 11B{1H} NMR (64 MHz) δ
Me3SiB(OC(CH3)2C(CH3)2O) (18): MS (EI) m/ z (relative
1
28
intensity) 185 (12.2) amu (M+
- -
12C1H3 for 12C9 H2111B16O2
Si), 157 (3.4), 143 (6.9), 125 (2.5), 117 (4.7), 101 (20.9), 84 (100),
75 (20.7), 73 (15.0), 69 (56.0), 55 (10.0).
Me3Si-CtC-B(OC(CH3)2C(CH3)2O) (19): MS (EI) m/ z
(relative intensity) 224 (19.6) amu (M+ for
C -
1H2111B16O2
12
28
11
Si), 209 (70.6), 195 (3.3), 181 (6.9), 167 (52.4), 149 (22.1), 139
(32.1), 125 (100), 117 (5.6), 109 (46.5), 103 (8.2), 97 (22.7), 93
(14.5), 85 (20.7), 83 (27.4), 75 (27.4), 73 (21.7), 67 (12.7), 55
(11.7).
(Me 3Si)C (B (OC (C H 3)2C (C H 3)2O))dC (B (OC (C H 3)2C -
(CH3)2O))2 (20): MS (EI) m/ z (relative intensity) 463 (1.4) amu
(M+
-
12C1H3 for
C
1H4511B316O628Si), 420 (0.8), 363 (0.8), 337
12
23
(6.1), 295 (5.5), 280 (1.9), 254 (1.3), 237 (8.7), 221 (2.2), 197
(2.2), 181 (3.9), 167 (1.3), 153 (2.8), 143 (1.7), 135 (2.4), 125
(1.7), 109 (3.2), 101 (5.1), 84 (100), 73 (15.7), 69 (23.0), 55 (16.8).
Me3SiB(1,2-O2C6H4) (21): MS (EI) m/ z (relative intensity)
31.3 (br, overlapped, 2B); MS (EI) m/ z 516 amu (M+ for
12
C
1H3811B216O6).
30
1
192 amu (M+ for 12C9 H1311B16O228Si, 4.0), 177 (100), 161 (1.1),
(Z)-(Me3Si)C(B(OC(CH 3)2C(CH 3)2O))dCB(OC(CH 3)2C-
(CH3)2O))-CtC(SiMe3) (13b): 1H NMR (200 MHz) δ 1.34 (s,
12H, (OC(CH3)2C(CH3)2O)), 1.31 (s, 12H, (OC(CH3)2C(CH3)2O)),
0.29 (s, 9H, Si(CH3)3), 0.20 (s, 9H, Si(CH3)3); 13C{1H} NMR (50
MHz) δ 107.9 (1C, CtC), 102.8 (1C, CtC), 84.2 (2C, (OC-
(CH3)2C(CH3)2O)), 83.6 (2C, (OC(CH3)2C(CH3)2O)), 25.4 (4C,
(OC(CH3)2C(CH3)2O)), 24.6 (4C, (OC(CH3)2C(CH3)2O)), -0.3
(3C, Si(CH3)3), -0.6 (3C, Si(CH3)3) (CsB resonances too broad
149 (6.3), 135 (36.8), 117 (3.5), 105 (3.4), 91 (20.2), 73 (9.4), 58
(17.4), 53 (3.5).
Ca ta lytic Rea ction s Mon itor ed by NMR Sp ectr oscop y.
In a typical catalytic NMR tube reaction, in an N2-filled
glovebox, an NMR tube was charged with 1-octyne (8a ; 13 mg,
0.118 mmol), compound 1a (31 mg, 0.130 mmol) or 1c (33 mg,
0.130 mmol), and catalyst (4, 5 mg, ∼5.7 mol %; 3b, 6 mg, ∼5
mol %, 6 × 10-6 mol). CDCl3 was used to rinse the vials
employed for weighing the reagents and then to top up the
NMR tube up to a premeasured volume (0.5 mL). The tube
was sealed and shaken and then placed in a warm water bath
set to 52 °C for a period of 5 min and then in the spectrometer
to observe); 11B{1H} NMR (64 MHz) δ 28.9 (br, overlapped,
2B); MS (EI) m/ z 448 amu (M+ for
C
1H4211B216O428Si2).
12
22
(Z,Z)-(4-MeO-C6H4)C(B(1,2-O2C6H4))dC(B(1,2-O2C6H4))C-
(B(1,2-O2C6H4))dC(4-Me-OC6H4)(B(1,2-O2C6H4)) (14a ): mp
233.9-234.8 °C; 1H NMR (200 MHz) δ 7.27 (d, J ) 8.7 Hz,
4H, MeOC6H4), 7.00 (br s, 8H, (1,2-O2C6H4)), 6.93 (br s, 8H,
1
set at 52 °C for an additional 5 min. The H NMR spectrum

5152 Organometallics, Vol. 15, No. 24, 1996
Ta ble 1. Da ta Collection a n d Str u ctu r e Solu tion a n d Refin em en t for 3a ,b a n d 5a ,b
Lesley et al.
3a
3b
5a
5b
formula
MW
C
48H38B2O4P2Pt‚C6D6
C56H54B2O4P2Pt
1069.64
C38H32B2O4P2Pt
831.29
C40H36B2O4P2Pt
859.34
1041.59
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
triclinic
P1h
triclinic
P1h
triclinic
P1h
monoclinic
C2/c
15.655(2)
10.4619(13)
22.305(3)
90
107.200(3)
90
3489.8(8)
4
11.0771(10)
11.2471(10)
20.909(2)
104.564(2)
90.118(2)
115.667(2)
2254.0(3)
2
10.359(7)
16.378(8)
16.684(11)
102.19(4)
107.79(3)
106.85(3)
2431(3)
10.9514(12)
12.1452(13)
13.4068(14)
97.716(3)
108.341(3)
93.200(2)
1668.1(3)
2
Z
2
dcalc (g cm-3
)
1.535
1.461
1.655
1.636
cryst size (mm)
cryst color
0.42 × 0.38 × 0.12
pale yellow
160
3.231
1036
0.08 × 0.08 × 0.02
colorless
160
2.998
1080
0.12 × 0.12 × 0.04
0.18 × 0.10 × 0.08
colorless
160
4.155
1704
yellow
temp (K)
160
4.343
820
µ (mm-1
F(000)
)
no. of rflns for cell refinement
θ range, deg
8734 (θ range 2.0-25.5°)
45 (θ range 1.0-23.5°)
5629 (θ range 2.0-25.5°) 4820 (θ range 2.0-25.4°)
2.03-25.52
1.58-25.41
1.62-25.46 1.91-25.55
index ranges
-13 e h e 13, -12 e k e -12 e h e 11, -19 e k e -13 e h e 8, -12 e k e -18 e h e 17, -12 e k e
12, -24 e l e 18 14, -19 e l e 19 13, -15 e l e 15 10, -27 e l e 26
9819 10 453 7234 7351
no. of rflns measd
no. of indep rflns
7114 (Rint ) 0.0383)
7592 (Rint ) 0.0512)
5258 (Rint ) 0.0443)
2913 (Rint ) 0.0440)
no. of rflns with I > 2σ(I)
max and min transmissn
weighting params a, b
no. of params
6918
6627
4927
2584
0.847, 0.525
0.0373, 7.4975
569
0.832, 0.692
0.0000, 29.5992
602
0.592, 0.498
0.0649, 6.4357
425
0.550, 0.470
0.0210, 45.1574
233
GOF on F2
1.072
1.189
1.078
1.128
final R indices (I > 2σ(I))
R1 ) 0.0326,
wR2 ) 0.0833
R1 ) 0.0337,
wR2 ) 0.0844
0.0014(2)
0.001
1.15, -1.67
R1 ) 0.0583,
wR2 ) 0.1217
R1 ) 0.0729,
wR2 ) 0.1364
0
0.001
1.31, -2.08
R1 ) 0.0416,
wR2 ) 0.1050
R1 ) 0.0453,
wR2 ) 0.1089
0.0021(4)
0.002
2.05, -2.31
R1 ) 0.0419,
wR2 ) 0.0896
R1 ) 0.0493,
wR2 ) 0.0937
0.00023(5)
0.010
R indices (all data)a
extinction coeff
largest shift/esd
largest diff peak and hole (e Å-3
)
1.11, -1.12
a
2
2
2 2
R ) ∑(|Fo| - |Fc|)/∑(|Fo|), Rw ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2}1/2, and GOF ) S ) {∑[w(Fo - Fc
)
]/(n - p)}1/2 for n reflections and p
parameters in the refinement.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3a
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5a
Bond Lengths
Bond Lengths
Pt(1)-B(1)
Pt(1)-B(2)
Pt(1)-P(1)
Pt(1)-P(2)
2.040(6)
2.058(6)
2.3543(12)
2.3465(12)
B(1)-O(1)
B(1)-O(2)
B(2)-O(3)
B(2)-O(4)
1.408(6)
1.416(7)
1.398(7)
1.408(7)
Pt(1)-B(1)
Pt(1)-B(2)
Pt(1)-P(1)
Pt(1)-P(2)
2.058(8)
2.048(8)
2.304(2)
2.332(2)
B(1)-O(1)
B(1)-O(2)
B(2)-O(3)
B(2)-O(4)
1.416(9)
1.421(9)
1.415(10)
1.387(9)
Bond Angles
Bond Angles
81.0(3)
B(1)-Pt(1)-B(2)
B(2)-Pt(1)-P(2)
B(2)-Pt(1)-P(1)
O(1)-B(1)-Pt(1)
O(3)-B(2)-Pt(1)
O(1)-B(1)-O(2)
77.1(2)
167.6(2)
85.3(2)
B(1)-Pt(1)-P(2)
B(1)-Pt(1)-P(1)
P(2)-Pt(1)-P(1)
O(2)-B(1)-Pt(1)
O(4)-B(2)-Pt(1)
O(3)-B(2)-O(4)
90.7(2)
160.1(2)
107.14(4)
121.4(4)
125.2(4)
108.4(5)
B(1)-Pt(1)-B(2)
B(2)-Pt(1)-P(1)
B(2)-Pt(1)-P(2)
O(1)-B(1)-Pt(1)
O(3)-B(2)-Pt(1)
O(1)-B(1)-O(2)
B(1)-Pt(1)-P(1)
B(1)-Pt(1)-P(2)
P(2)-Pt(1)-P(1)
O(2)-B(1)-Pt(1)
O(4)-B(2)-Pt(1)
O(3)-B(2)-O(4)
167.8(2)
103.8(2)
85.36(6)
130.6(5)
125.5(5)
108.8(6)
89.4(2)
174.2(2)
121.8(5)
125.5(5)
107.5(6)
130.5(4)
126.4(4)
108.1(4)
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3b
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5b
Bond Lengths
Bond Lengths
Pt(1)-B(1)
Pt(1)-B(2)
Pt(1)-P(1)
Pt(1)-P(2)
2.045(11)
2.046(13)
2.344(3)
2.353(3)
B(1)-O(1)
B(1)-O(2)
B(2)-O(3)
B(2)-O(4)
1.425(12)
1.406(12)
1.415(13)
1.412(13)
Pt(1)-B(1)
Pt(1)-P(1)
2.031(8)
2.339(2)
B(1)-O(1)
1.442(9)
1.402(9)
B(1)-O(2)
Bond Angles
76.5(4)
167.8(2)
91.4(2)
100.72(9)
B(1A)-Pt(1)-B(1)
B(1)-Pt(1)-P(1A)
B(1)-Pt(1)-P(1)
P(1A)-Pt(1)-P(1)
O(1)-B(1)-Pt(1)
O(1)-B(1)-O(2)
O(2)-B(1)-Pt(1)
126.3(5)
106.9(6)
126.7(5)
Bond Angles
77.2(4)
90.7(3)
164.0(3)
121.1(7)
123.5(7)
108.1(8)
B(1)-Pt(1)-B(2)
B(2)-Pt(1)-P(1)
B(2)-Pt(1)-P(2)
O(1)-B(1)-Pt(1)
O(3)-B(2)-Pt(1)
O(1)-B(1)-O(2)
B(1)-Pt(1)-P(1)
B(1)-Pt(1)-P(2)
P(2)-Pt(1)-P(1)
O(2)-B(1)-Pt(1)
O(4)-B(2)-Pt(1)
O(3)-B(2)-O(4)
163.8(3)
88.9(3)
104.37(10)
130.5(7)
128.1(8)
108.2(9)
Rea ction of [(P P h 3)2P t(η-C2H4)] w ith B2(1,2-O2C6H4)3.
A CDCl3 or C6D6 (0.5 mL) solution of B2(cat)3 (6, 23 mg, 6.7 ×
10-5 mol) was added via pipet to solid 4 (50 mg, 6.7 × 10-5
mol), and the resultant orange to deep red solutions were
analyzed by NMR spectroscopy. In CDCl3: 31P{1H} NMR δ
29.9 (s, J Pt-P ) 3368 Hz), 28.8 (s, J Pt-P ) 3021 Hz), minor
products (δ 26.5, 23.6, 14.7 ppm); 11B{1H} NMR δ 23.7 (sharp),
14.5 ppm (sharp, minor product, [B(cat)2]-); 1H NMR (hydride
region) δ -16.3 ppm (t, J P-H ) 13 Hz; J Pt-H ) 1197 Hz). In
C6D6 (a red insoluble oil formed at the base of the NMR tube):
31P{1H} NMR δ 30.6 (s, J Pt-P ) 3061 Hz), 23.1 ppm (minor
was recorded every 5 min for the first 30 min and then every
30 min until at least 3 half-lives had been completed. The
initial time at ambient temperature was assumed to be
negligible in terms of the progress of the reaction, and the
reaction time coordinate was corrected for the initial heating
period and variables such as total acquisition time and the
delay between collection of spectra. In reactions involving 5a ,b
ca. 5 mol % of catalyst was used.

Platinum(II)-Bis(boryl) Catalyst Precursors
Ta ble 6. Da ta Collection a n d Str u ctu r e Solu tion a n d Refin em en t for 10c,e a n d 14a
10c 10e 14a
C42H30B4O10
Organometallics, Vol. 15, No. 24, 1996 5153
formula
MW
C21H16B2O5
370.0
C26H18B2O4
416.02
737.90
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
16.3130(14)
12.8737(9)
8.8296(8)
90
103.927(6)
90
1799.8(3)
4
triclinic
P1h
triclinic
P1h
9.8189(11)
11.1751(12)
20.672(2)
81.699(3)
82.609(2)
66.367(2)
2050.0(4)
4
9.9576(13)
12.720(2)
15.041(2)
85.500(3)
82.553(3)
77.231(4)
1839.8(4)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
d
calc (g cm-3
)
1.365
1.348
1.332
cryst size
cryst color
temp (K)
0.24 {100} × 0.22 {110} × 0.24 {101h} 0.54 × 0.40 × 0.34
0.32 × 0.22 × 0.20
colorless
colorless
yellow
180
160
160
0.093
764
µ (mm-1
F(000)
)
0.095
0.088
768
864
no. of rflns for cell refinement
θ range (deg)
25 (θ range 11.0-16.0)
7176 (θ range 2.0-25.5)
4892 (θ range 2.1-27.5)
2.0-26.0
1.00-25.47
1.37-28.42
index ranges
0 e h e 20, 0 e k e 15, -10 e l e 10
-11 e h e 11, -10 e k e 13, -12 e h e 9, -16 e k e 16,
-21 e l e 24
8902
6449 (Rint ) 0.0289)
5999
-19 e l e -20
11301
7905 (Rint ) 0.0370)
5553
no. of rflns measd
no. of indep rflns
no. of rflns with I > 2σ(I)
max and min transmissn
weighting params a, b
no. of params
3658
3534 (Rint ) 0.014)
2627a
0.973, 0.960
0.0297, 0.8126
578
0.0353, 0.6302
508
270
2.35 on F
GOF
1.084 on F2
1.052 on F2
final R indices (I > 2σ(I))
R indices (all data)b
extinction coeff
R ) 0.0337, Rw ) 0.0336a
R ) 0.0446, Rw ) 0.0342
0.00109(7)
R1 ) 0.0352, wR2 ) 0.0863
R1 ) 0.0387, wR2 ) 0.0903
0.0098(7)
R1 ) 0.0454, wR2 ) 0.0971
R1 ) 0.0754, wR2 ) 0.1208
0.0066(9)
largest shift/esd
0.002
0.22, -0.15
0.001
0.19, -0.15
<0.001
0.22, -0.19
largest diff peak and hole (e Å-3
)
a
b
[F>6σ(F)]. For 10c, R ) ∑||Fo| - |Fc||/∑(|Fo|), Rw ) {∑w(|Fo| - |Fc|)2/∑[wFo2]}1/2, and GOF ) S ) {∑[w(|Fo| - |Fc|)2]/(n - p)}1/2; for
10e and 14a , see definition in Table 1.
Ta ble 7. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 10c
Ta ble 8. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 10e
Bond Lengths
molecule 1
molecule 2
C(1)-C(2)
C(2)-C(3)
C(1)-B(9)
C(2)-B(18)
1.348(2)
1.484(2)
1.526(2)
1.566(2)
B(9)-O(10)
B(9)-O(11)
B(18)-O(19)
B(18)-O(20)
1.388(2)
1.392(2)
1.386(2)
1.386(2)
Bond Lengths
1.353(2) C(51)-C(52)
C(1)-C(2)
C(1)-B(1)
C(2)-B(2)
C(1)-C(31)
C(2)-C(41)
B(1)-O(1)
B(1)-O(2)
B(2)-O(3)
B(2)-O(4)
1.358(2)
1.553(2)
1.562(2)
1.491(2)
1.497(2)
1.390(2)
1.384(2)
1.381(2)
1.388(2)
1.559(2)
1.551(2)
1.500(2)
1.500(2)
1.386(2)
1.389(2)
1.386(2)
1.393(2)
C(51)-B(3)
C(52)-B(4)
C(51)-C(81)
C(52)-C(91)
B(3)-O(5)
B(3)-O(6)
B(4)-O(7)
B(4)-O(8)
Bond Angles
C(2)-C(1)-B(9)
C(1)-C(2)-B(18)
C(1)-B(9)-O(10)
C(1)-B(9)-O(11)
124.4(1) C(1)-C(2)-C(3)
120.1(1) C(3)-C(2)-B(18)
124.6(1) C(2)-B(18)-O(19)
124.5(1) C(2)-B(18)-O(20)
123.6(1)
116.3(1)
123.0(2)
125.5(2)
O(10)-B(9)-O(11) 110.9(1) O(19)-B(18)-O(20) 111.4(1)
product); 11B{1H} NMR δ 22.4 (sharp), 15 ppm (minor); 1H
NMR (hydride region) δ -23.2 (t, J P-H ) 13.7 Hz; J Pt-H ) 1359
Hz).
Bond Angles
C(2)-C(1)-C(31) 121.64(13) C(81)-C(51)-C(52) 121.43(14)
C(2)-C(1)-B(1)
126.51(14) C(52)-C(51)-B(3)
119.28(14)
119.29(13)
C(31)-C(1)-B(1) 111.84(12) C(81)-C(51)-B(3)
X-r a y Cr ysta llogr a p h y. Crystal data and other informa-
tion on structure determination are given in Table 1 for the
platinum complexes 3a ,b and 5a ,b and in Table 6 for the bis-
and tetrakis(boronate esters) 10c,e and 14a . Measurements
for 10c were made on a Siemens P4 four-circle diffractometer
and for the other samples on a Siemens SMART CCD area-
detector diffractometer; in all cases, graphite-monochromated
Mo KR radiation was used (λ ) 0.710 73 Å). Crystals were
obtained by diffusion of a layer of hexanes into a CDCl3
solution for 5a ,b and 10c, into a C6D6 solution for 3a , and into
a THF solution for 14a and by slow evaporation of a CDCl3
solution for 3b. For all except 10c, the crystals were mounted
on a glass fiber with a coating of perfluoro polyether oil, cell
parameters were refined from the observed setting angles and
detector spot positions for selected reflections, and intensities
were measured from a series of frames each covering a 0.3°
oscillation in ω. The crystal of 10c was mounted on a glass
fiber with epoxy cement, cell parameters were refined from
the observed setting angles of selected reflections, and intensi-
ties were measured with ω scans. Absorption corrections were
C(1)-C(2)-C(41) 121.32(13) C(51)-C(52)-C(91) 123.58(14)
C(1)-C(2)-B(2)
121.72(14) C(51)-C(52)-B(4)
125.23(14)
111.03(12)
C(41)-C(2)-B(2) 116.91(13) C(91)-C(52)-B(4)
semiempirical for the platinum complexes, based on sets of
equivalent reflections measured at different azimuthal angles;
for 10c, a face-indexed correction was applied, and no absorp-
tion corrections were made for 10e and 14a .
The structures were solved by heavy-atom (3a ,b) and direct
(all others) methods and refined by full-matrix least-squares
techniques. For 10c the refinement was on F using reflections
with Fo > 6σ(Fo), to minimize ∑w(|Fo| - |Fc|)2, with weighting
w-1 ) σ2(Fo); the refined isotropic extinction parameter ø is
2
defined such that Fc is multiplied by (1 + 0.002øFc /(sin 2θ))-1/4
.
For the other structures, the refinement was on F2 of all
independent reflections, to minimize ∑w((Fo - Fc2)2, with
2
weighting w-1 ) σ2(Fo2) + (aP)2/bP, where P ) (Fo + 2Fc2)/3;
2
the refined isotropic extinction parameter ø is defined such
that Fc is multiplied by (1 + 0.001øFc2λ3/(sin 2θ))-1/4. In each
case, anisotropic displacement parameters were refined for all

5154 Organometallics, Vol. 15, No. 24, 1996
Lesley et al.
Ta ble 9. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 14a
Refined atomic coordinates and equivalent isotropic dis-
placement parameters are given in the Supporting Informa-
tion, and selected bond lengths and angles for the structures
are given in Tables 2-5 for the platinum complexes and in
Tables 7-9 for the bis- and tetrakis(boronate esters).
Bond Lengths
C(1)-C(2)
C(1)-B(1)
C(2)-B(2)
C(3)-B(3)
C(4)-B(4)
B(1)-O(2)
B(2)-O(4)
B(3)-O(7)
B(4)-O(9)
1.373(3)
1.541(3)
1.570(3)
1.565(3)
1.546(3)
1.389(2)
1.389(2)
1.393(2)
1.384(2)
C(1)-C(31)
C(2)-C(3)
C(3)-C(4)
C(4)-C(61)
B(1)-O(1)
B(2)-O(3)
B(3)-O(6)
B(4)-O(8)
1.486(3)
1.488(3)
1.362(2)
1.494(2)
1.389(3)
1.385(2)
1.382(2)
1.386(2)
Ack n ow led gm en t. T.B.M. thanks the NSERC of
Canada for research funding and J ohnson Matthey Ltd.
and E. I. du Pont de Nemours & Co., Inc., for generous
supplies of platinum salts, N.C.N. and W.C. thank the
EPSRC for support, G.L. and P.N. thank the British
Council (Ottawa) for a travel scholarship, P.N. thanks
the NSERC for a postgraduate scholarship, A.J .S.
thanks the EPSRC for a studentship, and T.B.M. and
N.C.N. thank the NSERC, The Royal Society (London),
and the University of Newcastle-upon-Tyne for support-
ing this collaboration through a series of travel grants.
We also thank Prof. S. Collins for the preliminary
molecular mechanics calculations, Mr. L. E. B. Taylor
for assistance with the electrospray MS studies, and
Profs. J . F. Hartwig and M. R. Smith III for com-
munication of results prior to publication.
Bond Angles
120.0(2)
C(2)-C(1)-C(31)
C(31)-C(1)-B(1)
C(1)-C(2)-B(2)
C(4)-C(3)-C(2)
C(2)-C(3)-B(3)
C(3)-C(4)-B(4)
C(2)-C(1)-B(1)
C(1)-C(2)-C(3)
C(3)-C(2)-B(2)
C(4)-C(3)-B(3)
C(3)-C(4)-C(61)
C(61)-C(4)-B(4)
119.3(2)
121.9(2)
118.5(2)
121.7(2)
120.7(2)
116.4(2)
120.7(2)
119.4(2)
121.2(2)
116.8(2)
122.8(2)
non-hydrogen atoms, and isotropic hydrogen atoms were
constrained to ride on their parent carbon atoms with fixed
bond lengths and idealized bond angles.
In the case of 3b, 2-fold disorder was resolved and refined
for one tert-butyl group. Similarly, disorder was modeled for
the backbone of the phosphine ligand in 5b. In 5b, the Pt atom
is constrained to lie on a crystallographic C2 axis. The
structure of 10e has two independent molecules in the asym-
metric unit. Programs were standard Siemens control and
integration software, versions 4 and 5 of SHELXTL,31 and local
programs.
Su p p or tin g In for m a tion Ava ila ble: Complete lists of
bond lengths and angles, anisotropic displacement parameters,
hydrogen atom parameters, and non-hydrogen atom param-
eters for 3a ,b, 5a ,b, 10c,e, and 14a (45 pages). Ordering
information is given on any current masthead page. Also,
these data have been deposited at the Cambridge Crystal-
lographic Data Centre.
(31) Sheldrick, G. M. SHELXTL Siemens Analytical X-ray Instru-
ments Inc., Madison, WI, 1990 and 1994.
OM950918C