Electrophilic methylplatinum complexes: First structure of a hydroxytris(pentafluorophenyl)borate complex

Article abstract of DOI:10.1021/om960834j

Treatment of [PtMe₂(bu₂bpy)] (bu₂bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) with B(C₆F₅)₃ in the presence of the ligand L gives, under anhydrous conditions, [PtMeL(bu₂bpy)][MeB-(C₆F₅)₃] {L = CO (1a), C₂H₄ (2a), PPh₃ (3a)}. Similar reactions performed in the presence of H₂O afford [PtMeL(bu₂bpy)][HOB(C₆F₅)₃] {L = CO (1b), C₂H₄ (2b), PPh₃ (3b)}. In the absence of L, the treatment of [PtMe₂(bu₂bpy)] with B(C₆F₅)₃ and H₂O gives [Pt{HOB(C₆F₅)₃}Me(bu₂bpy)] (4), the first published example of a hydroxytris(pentafluorophenyDborate complex. All of the complexes are fully characterized by NMR and IR spectroscopy and, in the case of complex 4, by an X-ray analysis which confirms the attachment of the [HOB(C₆F₅)₃]^- ligand to the square-planar platinum atom via a Pt-O bond of 2.062(2) ?. We propose that, in the presence of water, B(C₆F₅)₃ forms an adduct [H₂OB(C₆F₅)₃] (which acts as a strong acid H[HOB(C₆F₅)₃]) and this then protonates a Pt-Me bond of [PtMe₂(bu₂bpy)] forming CH₄ and [PtMe(bu₂bpy)]⁺[HOB(C₆F₅) ₃]^-. This protonolysis methodology provides an alternative route to the well-established electrophilic methyl-ligand abstraction by B(C₆F₅)₃ for the production of late transition-metal cations.

Full text of DOI:10.1021/om960834j

Organometallics 1997, 16, 525-530
525
Articles
Electr op h ilic Meth ylp la tin u m Com p lexes: F ir st
Str u ctu r e of a Hyd r oxytr is(p en ta flu or op h en yl)bor a te
Com p lex
Geoffrey S. Hill,† Ljubica Manojlovic-Muir,‡ Kenneth W. Muir,*,‡ and
Richard J . Puddephatt*,†
Departments of Chemistry, The University of Western Ontario,
London, Ontario, Canada N6A 5B7, and The University of Glasgow,
Glasgow G12 8QQ, Scotland
Received September 30, 1996X
Treatment of [PtMe2(bu2bpy)] (bu2bpy ) 4,4′-di-tert-butyl-2,2′-bipyridine) with B(C6F5)3
in the presence of the ligand L gives, under anhydrous conditions, [PtMeL(bu2bpy)][MeB-
(C6F5)3] {L ) CO (1a ), C2H4 (2a ), PPh3 (3a )}. Similar reactions performed in the presence
of H2O afford [PtMeL(bu2bpy)][HOB(C6F5)3] {L ) CO (1b), C2H4 (2b), PPh3 (3b)}. In the
absence of L, the treatment of [PtMe2(bu2bpy)] with B(C6F5)3 and H2O gives
[Pt{HOB(C6F5)3}Me(bu2bpy)] (4), the first published example of a hydroxytris(pentafluo-
rophenyl)borate complex. All of the complexes are fully characterized by NMR and IR
spectroscopy and, in the case of complex 4, by an X-ray analysis which confirms the
attachment of the [HOB(C6F5)3]- ligand to the square-planar platinum atom via a Pt-O
bond of 2.062(2) Å. We propose that, in the presence of water, B(C6F5)3 forms an adduct
[H2OB(C6F5)3] (which acts as a strong acid H[HOB(C6F5)3]) and this then protonates a Pt-
Me bond of [PtMe2(bu2bpy)] forming CH4 and [PtMe(bu2bpy)]+[HOB(C6F5)3]-. This proto-
nolysis methodology provides an alternative route to the well-established electrophilic methyl-
ligand abstraction by B(C6F5)3 for the production of late transition-metal cations.
Sch em e 1
In tr od u ction
There has been increasing interest in electrophilic
cationic transition-metal complexes as they often pos-
sess unique and highly desirable catalytic properties.
For example, early transition-metal metallocenium and
ansa-metallocenium cations1 as well as late transition-
metal cations of the type [MMe(N-N)]+ (M ) Ni, Pd;
N-N ) diimine)2 are highly active catalysts for the
polymerization of ethylene and R-olefins.
One of the most common methods used to produce
transition-metal cations is by direct electrophilic attack
on a M-Me bond by the powerful Lewis acid B(C6F5)3,
to produce [M]+[MeB(C6F5)3]-. This methodology was
introduced several years ago for creating vacant sites
in early transition-metal complexes3 but has only been
recently applied to late transition-metal systems.4 For
example, we have shown that under anhydrous condi-
tions, methyl-ligand abstraction from [PtMe2(bu2bpy)]
by B(C6F5)3 in the presence of the ligand L affords the
complexes [PtMeL(bu2bpy)][MeB(C6F5)3] {L ) CO (1a ),
C2H4 (2a ); bu2bpy ) 4,4′-di-tert-butyl-2,2′-bipyridine}4
and we now show that in the presence of PPh3 it leads
to the formation of [PtMe(PPh3)(bu2bpy)][MeB(C6F5)3]
(3a ) (Scheme 1).
In this paper we also report that in the presence of
water B(C6F5)3 does not directly attack a Pt-Me bond
of [PtMe2(bu2bpy)] but forms an adduct [H2OB(C6F5)3]
(which acts as a strong acid H[HOB(C6F5)3]) which
rapidly protonates a Pt-Me bond to form CH4 and the
proposed cationic intermediate [PtMe(bu2bpy)]+-
[HOB(C6F5)3]-. This protonation methodology provides
an alternative synthetic route to transition-metal cat-
ions which still uses B(C6F5)3 as the key reagent. The
† The University of Western Ontario.
‡ The University of Glasgow.
X Abstract published in Advance ACS Abstracts, J anuary 1, 1997.
(1) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(2) (a) Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc.
1996, 118, 4746. (b) J ohnson, L. K.; Mecking, S.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 267. (c) J ohnson, L. K.; Killian, C. M.;
Brookhart, M. J . Am. Chem. Soc. 1995, 117, 6414. (d) Rix, F. C.;
Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137. (e) Brookhart, M.;
Rix, F. C.; DeSimone, J . C.; Barborak, J . C. J . Am. Chem. Soc. 1992,
114, 5895.
(3) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991, 113,
3623.
(4) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J . J . Chem. Soc.,
Dalton Trans. 1996, 1809.
S0276-7333(96)00834-5 CCC: $14.00 © 1997 American Chemical Society

526 Organometallics, Vol. 16, No. 4, 1997
Hill et al.
with the exception of the 11B NMR which shows a
singlet at δ ) -4.4, indicative of the [HOB(C6F5)3]-
anion.7 The infrared spectra of complexes 1b, 2b, and
3b show a strong O-H stretching band at 3684 cm-1
that is absent in the otherwise very similar infrared
spectra of 1a , 2a , and 3a , respectively.
Sch em e 2
In the absence of the ligand L, the low-temperature
reaction of [PtMe2(bu2bpy)] with B(C6F5)3 and 1 equiv
of water produces CH4 and the {hydroxytris(penta-
fluorophenyl)borato}platinum(II) complex 4 in high
yield (Scheme 2).11 To our knowledge, the only other
example of a transition-metal complex incorporating the
[HOB(C6F5)3]- group is [(Cp*)2Ta(OH)Me][HOB(C6F5)3],
which is formed upon treatment of [(Cp*)2TaMe2]SO3-
CF3 with [NaB(C6F5)4] and in which the [HOB(C6F5)3]-
group is not coordinated.8 Thus, complex 4 provides the
first published example of a transition-metal complex
containing a coordinated [HOB(C6F5)3]- ligand, though
such species have been mentioned in the patent litera-
closest analogies to this system of which we are aware
employ either the trialkylammonium acid5 [HNBu3]+-
[B(C6F5)4]- or the oxonium acid6 [H(OEt2)2]+[{3,5-
(CF3)2C6H3}4B]-. The protonation of a zirconium-
methyl bond in [(Cp*)2ZrMe2] by [HNEt3][HOB(C6F5)3]
gives not a cationic species but the zirconoxyborane
[(Cp*)2ZrOB(C6F5)3].7
1
ture.7 The H NMR spectrum of complex 4 shows the
expected two tert-butyl resonances and six sets of
aromatic resonances due to the inequivalent nature of
the two pyridyl moieties of the bu2bpy ligand. The Pt-
Me ligand resonates at δ ) 0.81 with 2J (PtH) ) 78.9
Hz. The PtO(H)B group gives a broad resonance at δ
) 3.21 which does not show any resolvable splitting
even at -90 °C. No coupling of the PtO(H)B group to
195Pt is observed, and we assume that this is due to a
rapid exchange process. This PtO(H)B resonance disap-
pears upon treatment of an Et2O solution of complex 4
Resu lts a n d Discu ssion
Under anhydrous conditions, electrophilic methyl-
ligand abstraction from [PtMe2(bu2bpy)] by the powerful
Lewis acid B(C6F5)3 in the presence of the ligand L gives
the complexes [PtMeL(bu2bpy)][MeB(C6F5)3] {L ) CO
(1a ), C2H4 (2a ), PPh3 (3a ); bu2bpy ) 4,4′-di-tert-butyl-
2,2′-bipyridine}. The synthesis and characterization of
complexes 1a and 2a have been reported previously.4
Complex 3a is an orange hygroscopic solid that can be
isolated in good yield and has been characterized on the
basis of NMR spectroscopic (1H, 11B, and 31P) and
microanalytical data. The 1H NMR spectrum shows the
expected two tert-butyl resonances and six sets of
aromatic resonances due to the inequivalent nature of
the two pyridyl moieties of the bu2bpy ligand. The Pt-
Me ligand resonates at δ ) 0.71 with 2J (PtH) ) 72.0
Hz, typical of other cationic platinum(II) complexes.4
The 31P NMR spectrum shows the expected singlet at δ
) 20.0. This resonance is flanked by 195Pt satellite
1
with D2O and is absent in the otherwise identical H
NMR spectrum of [Pt{DOB(C6F5)3}Me(bu2bpy)] pre-
pared from [PtMe2(bu2bpy)], B(C6F5)3, and D2O. The
infrared spectrum of complex 4 shows a sharp O-H
stretching band at 3640 cm-1. This band is replaced
by a weak absorption at 2673 cm-1 in the infrared
spectrum of [Pt{DOB(C6F5)3}Me(bu2bpy)]. At room
temperature, rapid rotation about the O-B and B-C
bonds renders the three pentafluorophenyl moieties of
4 equivalent, and the 19F NMR spectrum shows only
three sets of resonances, one set for each of the ortho-,
meta-, and para-fluorine atoms. However, at -90 °C
these three sets resolve into eight separate resonances,
indicating that the three pentafluorophenyl moieties are
no longer equivalent. This low-temperature phenom-
enon is certainly a result of the steric interference
introduced upon coordination of the [HOB(C6F5)3]- ion
to platinum, since none of the compounds which contain
either the free [MeB(C6F5)3]- ion (in complexes 1a , 2a ,
3a ) or [HOB(C6F5)3]- ion (in complexes 1b, 2b, 3b)
shows any further resolution in the 19F NMR at -90
°C due to inequivalent pentafluorophenyl groups.
1
signals with J (PtP) ) 4343 Hz, typical of other cationic
platinum(II)-phosphine complexes.9 The 11B NMR
spectra of complexes 1a , 2a , and 3a show a singlet at δ
) -15.1, indicative of the [MeB(C6F5)3]- anion.3,7,10
During the initial preparations of complexes 1a , 2a ,
and 3a , it was noted that some of the corresponding
complex, [PtMeL(bu2bpy)][HOB(C6F5)3] {L ) CO (1b),
C2H4 (2b), PPh3 (3b)}, was often produced (Scheme 2).
The cause of this is most certainly the introduction of
adventitious H2O into the reaction vessel since these
[HOB(C6F5)3]- complexes are formed exclusively if 1
equiv of H2O is added during the initial stages of the
reaction. Complexes 1b, 2b, and 3b give very similar
NMR spectra to complexes 1a , 2a , and 3a , respectively,
The structure of 4 has been confirmed by X-ray
analysis (Figure 1). The cis-N2CO donor set which
surrounds the Pt atom departs significantly from ideal
square-planar coordination: as expected, the N-Pt-N
angle narrows to accommodate the restricted bite of the
bu2bpy ligand and there is also a slight tetrahedral
distortion, with donor atoms lying alternately 0.04 Å
above and below the coordination plane. The Pt-N
bond lengths (Table 1) differ by 0.117(3) Å, reflecting
the high trans-influence of σ-CH3 and the low trans-
(5) Yang, X.; Stern, C. L.; Marks, T. L. Organometallics 1991, 10,
840.
(6) (a) Brookhart, M.; Grant, B.; Volpe, J r., A. F. Organometallics
1992, 11, 3920. (b) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E.
Personal communication.
(7) (a) Siedle, A. R.; Newmark, R. A.; Lamanna, W. M.; Huffman,
J . C. Organometallics 1993, 12, 1491. (b) Siedle, A. R.; Lamanna, W.
M. PCT Int. Appl. WO 1993, 21,238 (Chem. Abs. 1994, 121, 36424x).
(8) Schaefer, W. P.; Quan, R. W.; Bercaw, J . E. Acta Crystallogr.
1993, C49, 878.
(9) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
(10) Siedle, A. R.; Newmark, R. A. J . Organomet. Chem. 1995, 497,
119.
(11) CH3D was detected by GC-MS when the reaction was performed
in the presence of D2O.

Electrophilic Methylplatinum Complexes
Organometallics, Vol. 16, No. 4, 1997 527
Ta ble 1. Selected Dista n ces (Å) a n d An gles (d eg)
in [P t{HOB(C6F 5)3}Me(bu 2bp y)], 4
(a) Bond Lengths
Pt1-O1
Pt1-N2
C21-B1
C41-B1
2.062(2)
2.097(2)
1.659(4)
1.636(4)
Pt1-N1
Pt1-C19
O1-B1
1.980(2)
2.037(3)
1.526(3)
1.654(3)
C31-B1
(b) Bond Angles
O1-Pt1-N1
O1-Pt1-C19
N1-Pt1-C19
Pt1-O1-N10
H1O-O1-B1
O1-B1-C31
C21-B1-C31
C31-B1-C41
172.6(1)
90.6(1)
96.1(1)
115(3)
O1-Pt1-N2
N1-Pt1-N2
N2-Pt1-C19
Pt1-O1-B1
O1-B1-C21
O1-B1-C41
C21-B1-C41
93.3(1)
80.1(1)
175.7(1)
128.2(2)
108.3(2)
103.2(2)
115.2(2)
111(3)
111.7(2)
104.3(2)
114.3(2)
(c) Torsion Angles
C19-Pt1-O1-B1
73.8(2) Pt1-O1-B1-C21
132.5(2)
10.0(3)
46.2(3)
170.5(2)
F igu r e 1. Molecular structure of [Pt{HOB(C6F5)3}Me(bu2-
bpy)], 4. Displacement ellipsoids of 30% are shown except
for hydrogen atoms which are displayed as spheres of
arbitrary size. The disorder of the methyl carbon atoms
attached to C11 is not illustrated. Phenyl carbon atoms
are numbered cyclically C21-C26, C31-C36, and C41-
C46, in each case starting from the atom bonded to B1.
The atoms F1-F5 are attached in sequence to C22-C26,
F6-F10 to C32-C36, and F11-F15 to C42-C46.
Pt1-O1-B1-C31 -113.2(2) Pt1-O1-B1-C41
C22-C21-B1-O1 -140.5(2) C26-C21-B1-O1
C32-C31-B1-O1
C42-C41-B1-O1
-14.0(4) C36-C31-B1-O1
70.2(3) C46-C41-B1-O1 -100.6(3)
(d) Hydrogen Bonds
bond
O‚‚‚F
O-H
H‚‚‚F
O-H‚‚‚F
O1-H1O‚‚‚F5
O1-H1O‚‚‚F6
2.722(3)
2.692(3)
0.67(4)
0.67(4)
2.32(4)
2.18(4)
120(4)
135(5)
influence of oxygen donor ligands,9,12 thereby confirming
less precise results of the only previous structural study
of a platinum(II) compound with a cis-(sp2-N)2CO donor
set.13 The Pt-O bond length in 4 [2.062(2) Å] is a little
longer than the mean Pt(II)-OH distance obtained from
a database survey [2.006 Å],14 while the reverse is true
of the Pt-CH3 distance [2.037(3) Å in 4 compared with
a database value of 2.107 Å].
The bu2bpy ligand contains two rigorously planar
pyridyl rings (rms, ∆ < 0.004 Å) twisted about the
central single bond [C5-C6 ) 1.476(3) Å] so that the
C4-C5-C6-C7 torsion angle is 6.9(4)°. This twist still
leaves a short H4‚‚‚H7 contact of 2.16 Å; it may explain
the tetrahedral distortion of the Pt coordination. The
acuteness of the endocyclic C-C-C angles at C3 and
C8 [115.7(3) and 115.8(2)°] can be attributed to electron
release by the tert-butyl substituents.15 Each of the
three methyl groups attached to C11 is disordered over
two sites with occupancy ratio ca. 4:1. The methyl
groups attached to C15 show physically unreasonable
displacement parameters [e.g. Umax ) 0.27 Å2 for C17]
suggestive of disorder which is not explicitly accounted
for in the final structural model.
to Pt: corresponding values in structures containing the
uncomplexed [HOB(C6F5)3]- anion are 1.487(3) Å in
[Et3NH][HOB(C6F5)3] and 1.490(10) Å in [(Cp*)2TaMe-
(OH)] [HOB(C6F5)3].7,8 It has been shown by a crystal
structure analysis of [H2OB(C6F5)3]‚2H2O that only one
water molecule is directly attached to boron, forming
the conjugate acid of [HOB(C6F5)3]-.16 However in
[ReVO2(C10H24N4)]Cl‚2[H2OBPh3] the B-O distance
[1.602(6) Å] is much longer than in 4.17 The only other
structure related to 4 of which we are aware is
[(Cp*)2ZrIV(OB(C6F5)3] in which the conjugate base of
[HOB(C6F5)3]- is bonded to zirconium through an ortho
fluorine atom as well as through oxygen [B-O 1.460(6)
Å]; the B-O-Zr angle of 151.2(3)° in this structure is
substantially more obtuse than the B-O-Pt angle of
128.2(2)° in 4.7 However, it may also be worth noting
here that there is a single structural report of the
2-
attachment of OBPh3 to a tungsten(VI) cation.18
The conformation of the [HOB(C6F5)3]- ligand in 4 is
such that B1 lies far from the coordination plane of the
metal atom (C19-Pt1-O1-B1 ) 74°). The Pt1-O1-
B1-C41 chain is nearly planar (torsion angle 10°) so
that the C41 ring lies above the coordination plane of
Pt1; however, the shortest contact between the C41 ring
and the metal [Pt1‚‚‚C41 ) 3.185(2) Å] is clearly
nonbonding. This arrangement leaves the face of the
Pt1 coordination plane opposite to the C41 ring rela-
tively exposed, and in consequence there is a short
intermolecular Pt‚‚‚Pt contact of 4.1201(4) Å with a
centrosymmetrically related molecule.
The [HOB(C6F5)3]- ligand in 4 is much the most novel
feature of the structure. The analysis allowed the
hydrogen atom attached to O1 to be successfully, though
not very accurately, located. The central boron atom
has a somewhat distorted tetrahedral coordination and
forms B-C bonds whose lengths [1.636(4)-1.659(4) Å]
cluster about the database mean14 for the corresponding
-
bonds in BPh4 (1.643 Å). The B-O bond length
One further feature of the conformation adopted by
the [HOB(C6F5)3]- ligand in 4 requires comment. The
OH group is contained in a cleft between the C21 and
C31 C6F5 rings so that a weak bifurcated intramolecular
[1.526(3) Å] may be slightly lengthened by coordination
(12) Manojlovic-Muir, Lj.; Muir, K. W. Inorg. Chim. Acta 1974, 10,
47.
(13) Dieck, H. T.; Fendesak, G.; Munz, C. Polyhedron 1991, 10, 255.
(14) International Tables for Crystallography; Vol. C, International
Union of Crystallography; Kluwer Academic Publishers: Dordrecht,
The Netherlands, 1992; Vol. C, Tables 9.5.1.1 and 9.6.3.3.
(15) Accurate Molecular Structures; Domenicano, A., Hargittai, I.,
Eds.; International Union of Crystallography; OUP: Oxford, U.K.,
1992; Chapter 18 and references therein. In particular: Domenicano,
A.; Vaciago, A.; Coulson, C. A. Acta Crystallogr. 1975, B31, 221.
(16) Siedle, A. R.; Lamanna, W. M.; Newmark, R. A.; Stevens, J .;
Richardson, D. E.; Ryan, M. Makromol. Chem. Macromol. Symp. 1993,
66, 215.
(17) Blake, A. J .; Greig, J . A.; Schroder, M. J . Chem. Soc., Dalton
Trans. 1988, 2645.
(18) Schreiber, P.; Wieghardt, K.; Nuber, B.; Weiss, J . Z. Naturfor-
sch. B 1990, 45, 619.

528 Organometallics, Vol. 16, No. 4, 1997
Hill et al.
Sch em e 3
hydrogen bond is formed involving F5 and F6 as
acceptors (Table 1d). Interestingly, the C-F5 and
C-F6 bond lengths [1.366(4) and 1.362(3) Å] are very
slightly longer than the other 13 C-F bond lengths
[1.343(4)-1.355(3) Å]. Although the 11 atoms of each
C6F5 ring barely deviate from planarity (rms ∆ < 0.02
Å) the displacements of the boron atom from the ring
planes [respectively 0.113(3), 0.026(3), and 0.186(3) Å
for the C21, C31, and C41 rings] are irregular and in
two cases highly significant. The acuteness of the
endocyclic C-C-C angles subtended by the atoms C21,
C31, and C41 [113.0(3)-113.5(3)°] is compensated by
an increase to 123.9(3)-124.5(3)° of the adjacent angles
at carbon atoms ortho to boron. These features have
been noted previously in the free [HOB(C6F5)3]- anion8
and may be ascribed to the difference in the electro-
negativities of B and F.15
would be the detection of the methyl(hydrido)platinum-
(IV) intermediate 5 (Scheme 3). In an attempt to detect
this intermediate, the reaction of B(C6F5)3 and water
with [PtMe2(bu2bpy)] in CD2Cl2 was monitored by low-
The [HOB(C6F5)3]- ligand in complex 4 is only weakly
coordinated to platinum as treatment of 4 with CO,
C2H4, and PPh3 gives the complexes 1b, 2b, and 3b,
respectively (Scheme 2). Similar complexes of the type
[PtMeX(bu2bpy)] (X ) O3SCF3, O2CCF3) do not react
with C2H4, illustrating that the [HOB(C6F5)3]- ligand
is an even poorer ligand than triflate or trifluoroacetate
for platinum.4
1
temperature H NMR spectroscopy (-90 °C). A reso-
nance was detected at δ ) -18.5, suggestive of a
(hydrido)platinum species.20,21 Unfortunately, the sta-
bility of this hydrido species was poor and at any given
time the concentration was not high enough to discern
the 195Pt satellite signals.22 Since the order of stability
toward CH4 reductive elimination from the methyl-
(hydrido)platinum(IV) complexes [PtX(H)Me2(bu2bpy)]
(X ) Cl, Br, I, O2CCF3, SO3CF3) follows the order of the
Pt-X bond strength, i.e. Cl > Br > I > O2CCF3, SO3-
CF3, it is not unexpected that complex 5, containing the
weakly bound [HOB(C6F5)3]- ion, would be highly
unstable.20 Nevertheless, this low-frequency resonance
in the 1H NMR spectrum is highly suggestive of a
transient (hydrido)platinum intermediate and, thus,
provides further evidence for the protonation mecha-
nism proposed in Scheme 3.
In the synthesis of complexes 1a , 2a , and 3a , B(C6F5)3
acts as a powerful Lewis acid and directly attacks a Pt-
Me bond in [PtMe2(bu2bpy)] to form [PtMe(Bu2bpy)]+-
[MeB(C6F5)3]-. However, in the presence of water a
different mechanism must be followed because the
corresponding [PtMe(bu2bpy)]+[HOB(C6F5)3]- complex
is preferentially formed. Although B(C6F5)3 has often
been described as a “water-tolerant Lewis acid”,19 it has
been shown that, in the presence of H2O, B(C6F5)3 forms
the hydrate [H2OB(C6F5)3]‚2H2O with one molecule of
H2O directly coordinated to boron.16 In the presence of
a suitable base, Nu, this hydrate can be deprotonated
to form the acid [HNu]+[HOB(C6F5)3]-.7,16 It has been
shown that the highly nucleophilic complex [PtMe2(bu2-
bpy)] reacts rapidly with a variety of protic acids,
resulting in protonation of the Pt-Me bond to initially
form CH4 and [PtMe(bu2bpy)]+.20 Thus, in the synthesis
of complexes 1b, 2b, and 3b, [PtMe2(bu2bpy)] most
probably acts as Nu and deprotonates H2OB(C6F5)3 to
form CH4 and [PtMe(bu2bpy)]+[HOB(C6F5)3]-. This
complex can either react with L to form [PtMeL(bu2-
bpy)][HOB(C6F5)3] {L ) CO (1b), C2H4 (2b), PPh3 (3b)}
or, in the absence of L, form the hydroxytris(pentafluo-
rophenyl)borate complex (4) (Scheme 2). In the reaction
with D2O in place of H2O, the organic products con-
tained CH3D but no CH2D2, indicating that exchange
between PtH and PtCH3 protons does not occur to a
significant extent in this reaction.21
It is has been suggested that the reaction of H2O with
[PtMe2(N-N)] (N-N ) 2,2′-bipyridine, 1,10-phenan-
throline) proceeds through the hydroxy(hydrido)plati-
num(IV) intermediate [PtH(OH)Me2(N-N)]23 (Scheme
4). It is thus conceivable that complex 5 is formed by
an initial reaction of H2O with [PtMe2(bu2bpy)], forming
[PtH(OH)Me2(bu2bpy)], which then reacts with B(C6F5)3
to give complex 5. However, the reaction of H2O with
[PtMe2(N-N)] is slow, taking several hours to reach
completion,23 whereas the reaction of Scheme 2 is very
rapid, so this mechanism can immediately be elimi-
nated. Since H[HOB(C6F5)3] is a strong acid, it is
expected to react with [PtMe2(bu2bpy)] much more
rapidly than water itself would.
Con clu sion s
In addition to the well-established methyl-ligand
abstraction by B(C6F5)3 to form [M]+[MeB(C6F5)3]-, we
have shown that, in the presence of water, B(C6F5)3
protonates a Pt-Me bond of [PtMe2(bu2bpy)] to form
[PtMe(bu2bpy)]+[HOB(C6F5)3]-. In the presence of the
It has been well established that the protonation of
the Pt-C bond follows an oxidative addition/reductive
elimination mechanism proceeding through an alkyl-
(hydrido)platinum(IV) intermediate.20,21 The most de-
finitive evidence for the proposed protonation mecha-
nism for the production of complexes 1b, 2b, 3b, and 4
(22) Monitoring similar reactions by low-temperature 1H NMR (-90
°C) with either CH3OH or C6H5OH in place of H2O resulted in no
observable hydride resonances.
(19) (a) Ishihara, K.; Hanaki, N.; Funahashi, M.; Miyata, M.,
Yamamoto, H. Bull. Chem. Soc. J pn. 1995, 68, 1721. (a) Yang, X.;
Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994, 116, 10015.
(20) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J . Organometallics
1995, 14, 4966.
(21) (a) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1995, 117, 9371; 1996, 118, 5961. (b) De Felice, V.; De Renzi, A.;
Panunzi, A.; Tesauro, D. J . Organomet. Chem. 1995, 488, C13.
(23) (a) Canty, A. J .; Fritsche, S. D.; J in, H.; Honeyman, R. T.;
Skelton, B. W.; White, A. H. J . Organomet. Chem. 1996, 510, 281. (b)
Canty, A. J .; Fritsche, S. D.; J in, H.; Skelton, B. W.; White, A. H. J .
Organomet. Chem. 1995, 490, C18. (c) Canty, A. J .; Honeyman, R. T.;
Roberts, A. S.; Traill, P. R.; Colton, R.; Skelton, B. W.; White, A. H. J .
Organomet. Chem. 1994, 471, C8. (d) Appleton, T. G.; Hall, J . R.;
Neale, D. W.; Williams, M. A. J . Organomet. Chem. 1984, 276, C73.
(e) Monaghan, P. K.; Puddephatt, R. J . Organometallics 1984, 3, 444.

Electrophilic Methylplatinum Complexes
Organometallics, Vol. 16, No. 4, 1997 529
Cl2, 25 °C): δ ) -124.5 [br s, 6F, o-F], -160.8 [m, 3F, p-F],
-165.8 [m, 6F, m-F]. 19F NMR (CD2Cl2, -90 °C): δ ) -132
(br m, 3F, o-F), -133 (s, 1F, o-F), -139 (s, 1F, o-F), -143 (s,
1F, o-F), -159 (s, 1F, p-F), -160 (br m, 2F, p-F), -164 (br m,
3F, m-F), -165 (br m, 3F, m-F). 195Pt NMR (CD2Cl2): δ )
-1330 [br s (∆ν1/2 ) ca. 400 Hz)]. IR (Nujol, cm-1): 3640 [s,
ν(OH)]. Anal. Calcd for C37H28BF15N2OPt: C, 44.0; H, 3.1;
N, 2.7. Found: C, 44.1; H, 2.8; N, 2.8.
Sch em e 4
Alter n a te Meth od for th e P r ep a r a tion of 4. To a
suspension of [PtMe2(bu2bpy)] (0.100 g, 0.203 mmol) in Et2O
(5.0 mL) at -78 °C was added a solution of B(C6F5)3 (0.105 g,
0.203 mmol) in Et2O (2.0 mL). The solution was stirred at
-78 °C until the color had completely changed from orange to
bright-yellow (ca. 2.0 h). The mixture was then allowed to
warm to room temperature, and the solvent was removed in
vacuo to give a yellow product. The product could be recrys-
tallized from CH2Cl2/n-pentane to afford a yellow microcrys-
talline solid. Yield: 0.189 g (93%).
ligand L (L ) CO, C2H4, PPh3) the corresponding
cationic complex, [PtMeL(bu2bpy)][HOB(C6F5)3], is
formed. However, in the absence of L, the [HOB(C6F5)3]-
anion coordinates to platinum to form the first published
example of a hydroxytris(pentafluorophenyl)borate com-
plex (4), which has been fully characterized by NMR
spectroscopy and X-ray crystallography. This procedure
provides an additional route to the production of late
transition-metal cations by the powerful Lewis acid
B(C6F5)3.
(4,4′-Di-ter t-bu tyl-2,2′-bipyr idin e)m eth yl(tr iph en ylph os-
p h in e)p la t in u m (II)
Met h ylt r is(p en t a flu or op h en yl)-
bor a te, [P tMeP P h 3(bu 2bp y)][MeB(C6F 5)3] (3a ). All glass-
ware must be flame-dried under vacuum prior to use. To a 50
mL Schlenk tube charged with PtMe2(bu2bpy)] (0.20 g, 0.405
mmol), B(C6F5)3 (0.208 g, 0.405 mmol), and PPh3 (0.106 g,
0.405 mmol) was added Et2O (10.0 mL). This bright orange
mixture was stirred at room temperature for ca. 24 h giving a
pale orange solution. Removal of the solvent in vacuo gave a
pale orange powder. Yield: 0.510 g (99%). 1H NMR (CD2-
Cl2): δ ) 8.89 [d, 1H, 3J (H6H5) ) 6.4 Hz, 3J (PtH) ) ca. 35 Hz,
H6], 8.88 [d, 1H, 3J (H6′H5′) ) 6.2 Hz, 3J (PtH) ) ca. 35 Hz, H6′],
Exp er im en ta l Section
4
8.20 (br s, 1H, H3), 8.11 [d, 1H, J (H3′H5′) ) 2.2 Hz, H3′], 7.78
Gen er a l P r oced u r es. All reactions were performed under
a N2 atmosphere using standard Schlenk techniques, unless
otherwise stated. All solvents were freshly distilled, dried, and
degassed prior to use. NMR spectra were recorded using a
Varian Gemini spectrometer (1H at 300.10 MHz, 11B at 64.17
MHz, 19F at 282.32 MHz, 31P at 121.44 MHz, and 195Pt at 42.99
MHz). Chemical shifts are reported in ppm with respect to
TMS (1H), BF3‚Et2O (11B), CFCl3 (19F), H3PO4/D2O (31P), or
K2[PtCl4]/D2O (195Pt). The 1H, 11B, 19F, 31P, and 195Pt NMR
spectra are referenced to the residual protons of the deuterated
solvents or to BF3‚Et2O, CFCl3, H3PO4/D2O, or K2[PtCl4]/D2O
contained in a coaxial insert, respectively. IR spectra (Nujol
mull) were recorded in the range 4000-400 cm-1 using a
Perkin-Elmer 2000 FT-IR instrument. Elemental analyses
were determined by Guelph Chemical Laboratories, Guelph,
Canada.
4
3
[m, 6H, PPh3)], 7.55 [dd, 1H, J (H5H3) ) 1.9 Hz, J (H5H6) )
6.4 Hz, H5], 7.50 (m, 9H, PPh3), 7.00 [dd, 1H, J (H5′H3′) ) 2.2
4
Hz, 3J (H5′H6′) ) 6.1, H5′], 1.49 [s, 9H, tert-bu), 1.32 (s, 9H, tert-
2
3
bu), 0.71 [s, 3H, J (PtH) ) 72.0 Hz, J (PtP) ) 3.7 Hz, Pt-Me].
11B NMR (CD2Cl2): δ ) -15.1 (br s). 31P NMR (CD2Cl2): δ )
20.0 [s, 1J (PtP) ) 4343 Hz]. Anal. Calcd for C56H45BF15N2-
PPt: C, 53.0; H, 3.6; N, 2.2 Found: C, 52.7; H, 3.5; N, 2.8.
Syn th esis of Com p lexes 1b, 2b, a n d 3b. The addition
of 1 equiv of H2O during the initial stages of the preparation
of complexes 1a , 2a , and 3a afforded exclusively complexes
1b, 2b, and 3b, respectively. The 1H NMR spectra of the
cationic platinum complexes are identical to those of the
analogous [MeB(C6F5)3]- complexes (1a , 2a , and 3a , respec-
tively). 11B NMR (CD2Cl2): δ ) -15.1. IR (Nujol, cm-1): 3684
[s, ν(OH)].
Cr ysta l str u ctu r e a n a lysis of 4: C37H28BF15N2OPt, fw )
1007.51, triclinic, space group P1h, a ) 10.7613(7) Å, b )
12.2174(11) Å, c ) 15.9389(7) Å, R ) 110.855(5)°, â )
96.347(4)°, γ ) 98.985(6)°, V ) 1902.7(2) Å3 [from setting
angles of 25 reflections with 20.7 e θ(Mo KR) e 22.3°], Z ) 2,
Dcalc ) 1.759 Mg/m3, µ ) 3.794 mm-1, F(000) ) 980.
The intensities of 12 786 reflections with 2.3 e θ(Mo KR) e
30° and -15 e h e 15, -17 e k e 2, and -21 e l e 22 were
measured at 20 °C from ω/2θ scans on an Enraf-Nonius CAD4
diffractometer with Mo KR X-rays, λ ) 0.710 73 Å, using a
yellow, needle-shaped crystal of dimensions 0.66 × 0.36 × 0.21
mm. The mean intensity of the three standard reflections
decreased by 9.4% during the experiment. Correction for this
decomposition and for absorption25 (analytical method,26 trans-
mission factors 0.32-0.53) and subsequent merging gave
11 037 independent reflections (Rint ) 0.015). Refinement of
F2 on 536 parameters using 11 036 observations converged (∆/σ
< 0.001) at R1 ) 0.025, wR2 ) 0.059 for 9203 reflections with
I > 2σ(I) and R1 ) 0.040, wR2 ) 0.065 for all 11 037 data with
[PtMe2(bu2bpy)],24 [PtMe(CO)(bu2bpy)][MeB(C6F5)3],4 and
[Pt(Me)(C2H4)(bu2bpy)][MeB(C6F5)3]4 were prepared by the
literature methods. B(C6F5)3 was obtained commercially
(Strem).
P r ep a r a t ion of Com p lexes. 4,4′-Di-ter t-b u t yl-2,2′-
b ip yr id in e {h yd r oxyt r is(p e n t a flu or op h e n yl)b or a t o}-
m eth ylp la tin u m (II), [P t{HOB(C6F 5)3}Me(bu 2bp y)] (4). All
glassware must be flame-dried under vacuum prior to use. To
a 100 mL Schlenk tube charged with [PtMe2(bu2bpy)] (10.0
mg, 0.020 mmol) and B(C6F5)3 (10.4 mg, 0.020 mmol) was
added Et2O (5.0 mL) and distilled H2O (0.4 µL, 0.02 mmol)
immediately producing an orange to yellow color change.
Removal of the solvent in vacuo and recrystallization from
CH2Cl2/n-pentane gave a bright yellow microcrystalline prod-
uct. Yield: 18.4 mg (92%). 1H NMR (CD2Cl2): δ ) 8.64 [d,
3
3
1H, J (H6H5) ) 6.3 Hz, J (PtH) ) ca. 60 Hz, H6], 8.50 [d, 1H,
3J (H6′H5′) ) 5.6 Hz, H6′], 7.91 [d, 1H, J (H3′H5′) ) 1.9 Hz, H3′],
4
7.84 [d, 1H, J (H3H5) ) 2.2 Hz, H3], 7.58 [dd, 1H, J (H5′H3′) )
4
4
1.9 Hz, J (H5′H6′) ) 5.7 Hz, H5′], 7.35 [dd, 1H, J (H5H3) ) 2.2
Hz, 3J (H5H6) ) 6.3, H5], 3.21 [br s, 1H, Pt-O(H)B], 1.41 (s,
9H, tert-bu), 1.39 (s, 9H, tert-bu), 0.81 [s, 3H, 2J (Pt-H) ) 78.9
Hz, Pt-Me]. 11B NMR (CD2Cl2): δ ) 0.1 (br s). 19F NMR (CD2-
3
4
(25) Computer programs used for data processing were as follows.
(a) GX: Mallinson, P. R.; Muir, K. W. J . Appl. Crystallogr. 1985, 18,
53. (b) PLATON: Spek, A. L. Acta Crystallogr. 1990, A46, 31.
(26) de Meulenaer, J .; Tompa, H. Acta Crystallogr. 1965, 19, 1014.
(24) Achar, S.; Scott, J . D.; Vittal, J . J .; Puddephatt, R. J . Organo-
metallics 1993, 12, 4592.

530 Organometallics, Vol. 16, No. 4, 1997
Hill et al.
|∆F| < 0.96 e‚Å-3 and w ) 1/[σ2(Fo2) + (0.0342P)2 + 0.72P],
in a difference map. Its positional and isotropic thermal
parameters were refined freely. Other hydrogen atoms rode
on their parent carbon atoms with C-H and U(H)iso set at
SHELXL default values.27 Atomic scattering factors and
dispersion corrections were taken from ref 28.
2
where P ) (Fo + 2Fc2)/3.27
In the final calculations the positional and anisotropic
displacement parameters of 57 non-hydrogen atoms (C37
-
BF15N2OPt), a scale factor, an extinction parameter, and
orientation parameters for seven methyl groups were refined
(Supporting Information). The C12-C14 methyl carbon atoms
were found to be disordered with site occupancy, R, of 0.794-
(5). The alternative sites C12*, C13*, and C14* were assigned
occupancies 1 - R and Uij parameters equal respectively to
those of C13, C12, and C14; only their positional parameters
were refined. Hydrogen atoms attached to C12*-C14* were
not included in the calculations. Despite the disorder of the
methyl groups, the hydrogen atom bonded to O1 was located
Ack n ow led gm en t. We thank the NSERC (Canada)
for financial support to R.J .P. and for a Post-graduate
Scholarship to G.S.H., EPSRC (U.K.) and the University
of Glasgow for support to K.W.M., and Dr. Louis
Farrugia for supplying PC versions of GX and PLATON.
Su p p or tin g In for m a tion Ava ila ble: For 4, tables of
atomic parameters and a complete geometry listing (9 pages).
Ordering information is given on any current masthead page.
X-ray data have also been deposited with the Cambridge
Crystallographic Data Centre.
(27) Sheldrick, G. M. SHELXL-93. A Program for the Refinement
of Crystal Structures, University of Go¨ttingen, Germany, 1993.
(28) International Tables for Crystallography; International Union
of Crystallography; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1992; Vol. C, Tables 4.2.6.8. and 6.2.1.1.
OM960834J