Synthesis, structure, and reactivity of an unusual platinum olefin carbene complex, [(η4-cod)Pt{=C(Ph2P=NSiMe3) 2-κC,κN}]

Article abstract of DOI:10.1021/om030003v

The organolithium dimer [Li₂C(Ph₂P=NSiMe ₃)₂]₂ ([Li₂-1]₂) reacts with 2 equiv of [PtCl₂-(cod)] (cod = 1,5-cyclooctadiene) in Et ₂O solution to give the novel Pt-carbene complex [(η ⁴-cod)Pt{=C(Ph₂P=NSiMe₃) ₂κ-C, κN}] (2), which is characterized by a relatively long Pt-C(carbene) bond and relatively short Pt-C(olefin) interactions indicative of an electron-rich Pt center. Under oxygen- and moisture-free conditions, 2 is remarkably inert; the cod ligand is not displaced by either monodentate or bidentate phosphines, phosphine sulfide, phosphite, or pyridine at room temperature, nor is the four-membered C,N-chelate ring opened by these reagents. However, 2 reacts with the electrophiles MeOTf (OTf = trifluoromethanesulfonate) and CO₂. In the former case, the uncoordinated N atom of 2 is methylated to form [η ⁴-cod)Pt{=C(Ph₂P=NSiMe₃)(Ph ₂P=N(Me)SiMe₃-κC,κN}][OTf] (3). In the latter, initial nucleophilic attack by the uncoordinated N atom on CO₂, followed by trimethylsilyl group migration from N to O, gives [(η ⁴-cod)Pt{=C(Ph₂P=NSiMe₃)(Ph ₂P=NC(O)OSiMe₃-κC,κN}] (4). Heating a benzene solution of 2 to 100°C in a sealed tube for several hours, or to 60°C for 10 min in the presence of H₂O, yields the ortho-metalated complex [(η⁴-cod)Pt{CH(Ph(C₆H₄)P=NSiMe ₃)(Ph₂P=NSiMe₃)-κC,κC′}] (5), which is characterized by Pt-C distances that are in the typical range for Pt-C(alkyl) and Pt-C(arene) interactions. The diastereoselectivity of the ortho metalation is consistent with an oxidative addition (nucleophilic) reaction mechanism for the ortho metalation. In contrast to 2, 5 displays typical cod substitution reactivity with chelating phosphines. The reaction between [Li ₂-1]₂ and [PtCl₂(cod)] in C₆H ₆ solution proceeds only very slowly and gives [Li][Pt{CH-(Ph(C ₆H₄)P=NSiMe₃)(Ph₂P=NSiMe ₃)-κC,κC′}{CH(Ph₂P=NSiMe ₃)₂-κC,κN}] (7) in low yield.

Full text of DOI:10.1021/om030003v

2832
Organometallics 2003, 22, 2832-2841
Syn th esis, Str u ctu r e, a n d Rea ctivity of a n Un u su a l
P la tin u m Olefin Ca r ben e Com p lex,
[(η4-cod )P t{dC(P h 2P dNSiMe3)2-KC,KN}]
Nathan D. J ones,† Guanyang Lin, Robert A. Gossage,‡ Robert McDonald,§ and
Ronald G. Cavell*
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Received J anuary 3, 2003
The organolithium dimer [Li2C(Ph2PdNSiMe3)2]2 ([Li2-1]2) reacts with 2 equiv of [PtCl2-
(cod)] (cod ) 1,5-cyclooctadiene) in Et2O solution to give the novel Pt-carbene complex [(η4-
cod)Pt{dC(Ph2PdNSiMe3)2-κC,κN}] (2), which is characterized by a relatively long Pt-
C(carbene) bond and relatively short Pt-C(olefin) interactions indicative of an electron-
rich Pt center. Under oxygen- and moisture-free conditions, 2 is remarkably inert; the cod
ligand is not displaced by either monodentate or bidentate phosphines, phosphine sulfide,
phosphite, or pyridine at room temperature, nor is the four-membered C,N-chelate ring
opened by these reagents. However, 2 reacts with the electrophiles MeOTf (OTf )
trifluoromethanesulfonate) and CO2. In the former case, the uncoordinated N atom of 2 is
methylated to form [(η4-cod)Pt{dC(Ph2PdNSiMe3)(Ph2PdN(Me)SiMe3-κC,κN}][OTf] (3). In
the latter, initial nucleophilic attack by the uncoordinated N atom on CO2, followed by
trimethylsilyl group migration from N to O, gives [(η4-cod)Pt{dC(Ph2PdNSiMe3)(Ph2Pd
NC(O)OSiMe3-κC,κN}] (4). Heating a benzene solution of 2 to 100 °C in a sealed tube for
several hours, or to 60 °C for 10 min in the presence of H2O, yields the ortho-metalated
complex [(η4-cod)Pt{CH(Ph(C6H4)PdNSiMe3)(Ph2PdNSiMe3)-κC,κC′}] (5), which is character-
ized by Pt-C distances that are in the typical range for Pt-C(alkyl) and Pt-C(arene)
interactions. The diastereoselectivity of the ortho metalation is consistent with an oxidative
addition (nucleophilic) reaction mechanism for the ortho metalation. In contrast to 2, 5
displays typical cod substitution reactivity with chelating phosphines. The reaction between
[Li2-1]2 and [PtCl2(cod)] in C6H6 solution proceeds only very slowly and gives [Li][Pt{CH-
(Ph(C6H4)PdNSiMe3)(Ph2PdNSiMe3)-κC,κC′}{CH(Ph2PdNSiMe3)2-κC,κN}] (7) in low yield.
In tr od u ction
1 forms a carbene-like M-C bond stabilized by chelation
of both N atoms to the metal. Structural studies show
that the pincer carbene systems have short metal-
carbon interactions indicative of MdC(carbene) double
bonds and that there is a substantial ylidic character
to the bonding within the framework of the ligand 1.
Single-point calculations at the density functional level
for [Zr(CH2Ph)2{dC(Ph2PdNSiMe3)2-κC,κN,κN′}] reveal
an appreciable negative charge on the carbene C atom
as well as positive charge on the P atoms,6 and indeed
related group 4 chlorides (Scheme 1) behave like Schrock-
type (nucleophilic) carbenes in that they undergo [2 +
Some time ago, we1,2 and others3 reported the syn-
thesis and characterization of the structurally unusual
organolithium complex [Li2C(Ph2PdNSiMe3)2]2 ([Li2-
1]2), which can be obtained by double deprotonation of
the methylene C atom of CH2(Ph2PdNSiMe3)2 (H2-1)4,5
using alkyl- or aryllithium reagents. Recently, we have
employed [Li2-1]2 and H2-1 in the synthesis of a number
of novel “pincer” carbene complexes of the group 4
metals6-10 and lanthanides,11 as well as bridging car-
bene complexes of Cr12 and Al.13 In all of these systems,
* To whom correspondence should be addressed. E-mail: ron.cavell@
ualberta.ca. Fax: 1-780-492-8231.
(6) Babu, R. P. K.; McDonald, R.; Decker, S. A.; Klobukowski, M.;
Cavell, R. G. Organometallics 1999, 18, 4226-4229.
(7) Babu, R. P. K.; McDonald, R.; Cavell, R. G. Chem. Commun.
2000, 481-482.
† Izaak Walton Killam Memorial Postdoctoral Fellow (2002-2003).
‡ Petroleum Research Fund Summer Research Fellow (2002). Per-
manent address: Department of Chemistry, Acadia University, Wolfville,
Nova Scotia, Canada B4P 2B3.
(8) Babu, R. P. K.; McDonald, R.; Cavell, R. G. Organometallics
2000, 19, 3462-3465.
§ X-ray crystallography laboratory.
(1) Kasani, A.; Babu, R. P. K.; McDonald, R.; Cavell, R. G. Angew.
Chem., Int. Ed. 1999, 38, 1483-1484.
(2) Klobukowski, M.; Decker, S. A.; Lovallo, C. C.; Cavell, R. G.
Theochem-J . Mol. Struct. 2001, 536, 189-194.
(3) Ong, C. M.; Stephan, D. W. J . Am. Chem. Soc. 1999, 121, 2939-
2940.
(4) Appel, V. R.; Ruppert, I. Z. Anorg. Allg. Chem. 1974, 406, 131-
144.
(5) Mu¨ller, A.; Mo¨hlen, M.; Neumu¨ller, B.; Faza, N.; Massa, W.;
Dehnicke, K. Z. Anorg. Allg. Chem. 1999, 625, 1748-1751.
(9) Cavell, R. G.; Babu, R. P. K.; Kasani, A.; McDonald, R. J . Am.
Chem. Soc. 1999, 121, 5805-5806.
(10) Kasani, A.; Babu, R. P. K.; McDonald, R.; Cavell, R. G. Angew.
Chem., Int. Ed. 2001, 40, 4400-4402.
(11) Kasani, A.; Ferguson, M.; Cavell, R. G. J . Am. Chem. Soc. 2000,
122, 726-727.
(12) Kasani, A.; McDonald, R.; Cavell, R. G. Chem. Commun. 1999,
1993-1994.
(13) Kasani, A.; McDonald, R.; Ferguson, M.; Cavell, R. G. Orga-
nometallics 1999, 18, 4241-4243.
10.1021/om030003v CCC: $25.00 © 2003 American Chemical Society
Publication on Web 06/10/2003

An Unusual Platinum Olefin Carbene Complex
Organometallics, Vol. 22, No. 14, 2003 2833
Sch em e 1. Rea ction s of Gr ou p 4 “P in cer ”
Ca r ben es w ith Isocya n a tes a n d Ca r bod iim id es
other is “dangling.” The sum of the angles around the
carbene C atom in 2 is 360°; C(1), P(1), P(2), and Pt form
a perfect plane. Complexes that contain chelating C,N
ligands where C is carbenic are relatively rare; other
examples are the recently discovered Ru-aminocarbene
complexes [RuCp(L)(dCPhNHpy-κC,κN)][PF6] (L ) CH3-
CN, PMe3; py ) o-pyridyl)16 and the tris(pyrazolyl)-
borate ruthenium carbenes derived from terminal
alkynes and 2-aminopyridines.17
The Pt-C(carbene) distance in 2 is 2.021(5) Å, ap-
preciably longer than those typically found for both
NHC complexes of two- and four-coordinate Pt (1.93-
1.97 Å)18-20 and Fischer carbene complexes of four-
coordinate Pt (1.87-1.96 Å).21-26 Indeed, the Pt-
C(carbene) distance in 2 is unusual in that it is more
akin to those found for Fischer carbene complexes of
five-27 and six-coordinate28 Pt (1.99-2.01 Å). Neverthe-
less, the Pt-C(carbene) bond in 2 is still shorter than
typical Pt-C(alkyl) single bonds (2.07-2.15 Å).29 Such
partial multiple-bond character may be the result of
π-electron delocalization within the ligand framework.
The intraligand distances of bound 1 merit discussion
in this regard. Both of the P-C(carbene) lengths in 2,
particularly that of the endocyclic bond, are considerably
shorter than that found for P-C(methylene) in H2-15
(1.697(5) (endo) and 1.721(5) (exo) vs 1.827(1) Å), while
the P-N distances, again particularly that of the
endocyclic bond, are appreciably longer (1.631(4) (endo)
and 1.550(4) Å (exo) vs 1.539(2) Å). In addition, the
Pt-N bond in 2 (2.092(4) Å) is shorter than those of the
related Pt complexes [PtCl(PEt3){CH(Ph2PdN-p-tolyl)-
(Ph2PNH-p-tolyl)-κC,κN}][PtCl3(PEt3)] (2.124(8) Å)30 and
[PtCl(PPhMe2){CH(Ph2PdN-p-tolyl)2-κC,κN}] (2.132(4)
Å)31 but identical in length with that of [PdCl2(Me3SiNd
PEt3)2] (2.095 Å).32 This may reflect either partial
double-bond character of the Pt-N bond or simply the
2] cycloaddition reactions with isocyantes and carbodi-
imides.8
The recent report of the application of the N-hetero-
cyclic carbene (NHC) complexes [Pt(η4-O(Me2SiCHd
CH2)2)(NHC)] to hydrosilylation catalysis14,15 provides
impetus for investigation into the synthesis and reactiv-
ity of other types of Pt-carbene complexes, especially
those involving chelating diolefins as ancillary ligands.
Herein, we report the first development of late-
transition-metal chemistry incorporating 1. We describe
the synthesis and structural characterization of an
intriguing Pt(II) compound, [(η4-cod)Pt{dC(Ph2Pd
NSiMe3)2-κC,κN}] (2), and compare and contrast its
bonding and reactivity with those of its early-transition-
metal counterparts. Because the formally dianionic
ligand 1 coordinates via a single four-membered C,N-
chelate in 2, the complex represents the first example
we have encountered in the use of 1 that is not a
classical “pincer” or bridging carbene, and indeed this
and other factors yield novel reactivity patterns. We
report the reactions of 2 with nucleophiles and electro-
philes, including heteroallenes, and the synthesis, struc-
tural characterization, and preliminary reactivity stud-
ies of the ortho-metalated complex [(η4-cod)Pt{CH(Ph-
(C6H4)PdNSiMe3)(Ph2PdNSiMe3)-κC,κC′}] (5).
(16) Standfest-Hauser, C. M.; Mereiter, K.; Schmid, R.; Kirchner,
K. Organometallics 2002, 21, 4891-4893.
(17) Ruba, E.; Hummel, A.; Mereiter, K.; Schmid, R.; Kirchner, K.
Organometallics 2002, 21, 4955-4959.
(18) Hasan, M.; Kozhevnikov, I. V.; Rafiq, M.; Siddiqui, H.; Femoni,
C.; Steiner, A.; Winterton, N. Inorg. Chem. 2001, 40, 795-800.
(19) Ku, R.-Z.; Huang, J .-C.; Cho, J .-Y.; Kang, F.-M.; Reddy, K. R.;
Chen, Y.-C.; Lee, K.-J .; Lee, J .-H.; Lee, G.-H.; Peng, C.-M.; Liu, S.-T.
Organometallics 1999, 18, 2145-2154.
(20) Arduengo, A. J .; Gamper, S. F.; Calabrese, J . C.; Davidson, F.
J . Am. Chem. Soc. 1994, 116, 4391-4394.
(21) Ferguson, G.; Li, Y.; McAlees, A. J .; McCrindle, R.; Xiang, K.
Organometallics 1999, 18, 2428-2439.
(22) Tollari, S.; Cenini, S.; Penoni, A.; Granata, G.; Palmisano, G.;
Demartin, F. J . Organomet. Chem. 2000, 608, 34-41.
(23) Ferguson, G.; Li, Y.; McAlees, A. J .; McCrindle, R.; Zang, E. J .
Organomet. Chem. 2001, 617-618, 671-680.
(24) Belluco, U.; Bertani, R.; Fornasiero, S.; Michelin, R. A.; Mozzon,
M. Inorg. Chim. Acta 1998, 275-276, 515-520.
(25) Barefield, E. K.; Carrier, A. M.; Sepelak, D. J .; Derveer, D. G.
V. Organometallics 1982, 1, 103-110.
(26) Anderson, G. K.; Cross, R. J .; Manojlovic-Muir, L.; Muir, K. W.;
Wales, R. A. J . Chem. Soc., Dalton Trans. 1979, 684-690.
(27) Cucciolito, M. E.; Panunzi, A.; Ruffo, F. Organometallics 1999,
18, 3482-3489.
(28) Redina, L. M.; Vittal, J . J .; Puddephatt, R. J . Organometallics
1995, 14, 1030-1038.
(29) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1-S83.
(30) Avis, M. W.; Vrieze, K.; Ernsting, J . M.; Elsevier, C. J .;
Veldman, N.; Spek, A. L.; Katti, K. V.; Barnes, C. L. Inorg. Chem. 1995,
34, 4092-4105.
(31) Avis, M. W.; Vrieze, K.; Ernsting, J . M.; Elsevier, C. J .;
Veldman, N.; Spek, A. L.; Katti, K. V.; Barnes, C. L. Organometallics
1996, 15, 2376-2392.
(32) Miekisch, T.; Mai, H. J .; Meyer, R.; Kocker, R. M. Z.; Dehnicke,
K.; Magull, J .; Goesmann, H. Z. Anorg. Allg. Chem. 1996, 622, 583-
588.
Resu lts a n d Discu ssion
Reaction of [Li2-1]2 with 2 equiv of [PtCl2(η4-cod)] in
Et2O gives [(η4-cod)Pt{dC(Ph2PdNSiMe3)2-κC,κN}] (2)
as a red-orange crystalline powder in 50% isolated yield
(Scheme 2). The analogous reaction conducted in C6H6
proceeds differently and will be discussed below. At-
tempts to prepare similar complexes starting from
[PtCl2(nitrile)2] (nitrile ) MeCN, PhCN) and cis-[PtCl2-
(PPh3)2] have so far been unsuccessful.
An ORTEP representation of the molecular structure
of 2 is shown in Figure 1; selected relevant bond lengths
and angles are given in Table 1. The coordination
enviroment around the Pt atom is a slightly distorted
square plane. The ligand 1 adopts a κC,κN coordination
mode in which one of the two N atoms of the ligand is
involved in a four-membered chelate with Pt, and the
(14) Marko´, I. E.; Ste´rin, S.; Buisine, O.; Mignani, G.; Branlard, P.;
Tinant, B.; Declercq, J .-P. Science 2002, 298, 204-206.
(15) Marko´, I. E.; Ste´rin, S. Patent WO 2001042258 (Rhodia Chemie,
France), 2001.

2834 Organometallics, Vol. 22, No. 14, 2003
J ones et al.
Sch em e 2. Syn th esis a n d Rea ction s of th e P t-Ca r ben e Com p lex [(η4-cod )P t{dC(P h 2P dNSiMe3)2-KC,KN}]
(2)a
a
Labels for the trimethylsilyl groups in 2 and 4 are discussed in the text. Reactions were conducted at room temperature
1
unless otherwise indicated. Reagents, solvents, and conditions: (i) /2 [Li2-1]2, Et2O; (ii) MeOTf, Et2O; (iii) CO2 (1 atm), hexanes;
(iv) 100 °C, 20 h, C6H6, or 60 °C, 10 min, C6H6 with 5 equiv of added H2O; (v) dppe, C6H6; (vi) LiH-1, C6H6, and also from PtCl2(cod)
and 1/2 [Li2-1]2 in C6H6 over days (see Experimental Section).
strong Lewis basicity of silylated phosphineimines. We
have previously postulated an electronically delocalized
model to account for structural differences between H2-1
and bound 1.2-6 Despite the great differences in metallic
electron density between 2 and the pincer carbene
complexes MCl2(1-κC,κN,κN′) (M ) Ti, Zr, Hf), the
endocyclic P-N bond in 2 (1.631(4) Å) is remarkably
similar to the average of those found in the group 4
complexes, which are 1.621(4),9 1.630(6),9 and 1.637(5)
Å,7 respectively. The endocyclic P-C bond length is also
similar, but less so: viz., 1.697(5) Å vs 1.679(4), 1.666-
(7) and 1.666(7) Å, respectively. These observations are
consistent with our previous assertions of π-electron
delocalization. In the case of 2 this is especially, but not
exclusively, manifest within the four-membered C,N
chelate. A more apt description of the bonding in 2 may
be that given in Chart 1.
An asymmetrically bound η4-cod ligand is also present
in 2. There is considerable difference between the
lengths of the Pt-C(olefin) bonds trans to the N-donor
atom (C(2) and C(3), average 2.145(5) Å) and those trans
to the carbene C atom (C(6) and C(7), average 2.212(5)
Å), suggesting a higher trans influence for the latter
donor atom. For reasons that are not immediately
obvious, the olefinic C atoms C(2) and C(3) are bound
symmetrically to the Pt center (Pt-C(2) ) 2.142(5) Å,
Pt-C(3) ) 2.147(5) Å), while those of the other alkene
are bound in a distinctly asymmetric fashion (Pt-C(6)
) 2.200(5) Å, Pt-C(7) ) 2.223(5) Å).
The Pt-C(olefin) distances in 2 are shorter than
average for other Pt-cod complexes (2.230 Å),29 consis-
tent with an electron-rich Pt center that strongly binds
π-acceptor ligands such as olefins. These structural
observations are in accord with the relative stability of

An Unusual Platinum Olefin Carbene Complex
Organometallics, Vol. 22, No. 14, 2003 2835
calculations, we believe that 2 may represent a rare
example of a square-planar, 18-electron Pt(II) complex,
in which the ligand 1 bears a formal 2- charge.
However, we cannot discount the possibility of neutral
1 coordinated to Pt(0).
NMR spectroscopic characterization reveals that the
solid-state structure of 2 is likely retained in solution.
As expected, there are two chemically inequivalent P
2
2
atom environments (δP 65.5 (d, J PP ) 67 Hz, J PPt
)
2
2
528 Hz), -1.1 (d, J PP ) 67, J PPt ) 0 Hz)) as well as
two correspondingly inequivalent SiMe3 proton environ-
ments (δH -0.01 (s), 0.48 (s)). The upfield phosphorus
resonance falls at a frequency similar to that of the two
equivalent P atoms of H2-1 (δP -4.2), suggesting that
this upfield doublet corresponds to the P atom of bound
1, whose corresponding N atom is not coordinated to
the metal center. In contrast to the upfield resonance
for which P-Pt coupling is zero, the low-field signal has
distinct 195Pt (I ) 1/2; 33.7% natural abundance) “satel-
lites.” This suggests that the P-Pt coupling is mediated
via the PdN-Pt rather than the P-CdPt linkage. The
195Pt{1H} NMR spectrum is consistent with this, in that
F igu r e 1. ORTEP representation (20% ellipsoids) of the
molecular structure of 2. Hydrogen atoms and all but the
ipso carbon atoms of the phenyl rings have been omitted
for clarity.
2
it shows a doublet (δPt 1136, J PtP ) 521 Hz) and not
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2 w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
the doublet of doublets that would arise from coupling
to two inequivalent P atoms. In addition, a 31P TROESY
experiment shows that the bound and free N atoms of
2 do not exchange chemically (during 0.4 s). This is
likely due to the strong, partial-double Pt-N bond.
Notably, the N atoms of the Pt-alkanide complexes
[PtCl(PR3){CR′(Ph2PdNR′′)2-κC,κN}], reported by Else-
vier and co-workers,31 are indeed in chemical exchange
and become equivalent on the NMR time scale at 293
K. The strong Pt-N bond in our complexes has impor-
tant ramifications for their chemistry.
Pt-N(1)
2.092(4)
2.142(5)
2.200(5)
1.631(4)
1.550(4)
Pt-C(1)
Pt-C(3)
Pt-C(7)
P(1)-C(1)
P(2)-C(1)
2.021(5)
2.147(5)
2.223(5)
1.697(5)
1.721(5)
Pt-C(2)
Pt-C(6)
P(1)-N(1)
P(2)-N(2)
N(1)-Pt-C(1)
N(1)-P1-C(1)
P(1)-C1-P(2)
75.2(2)
97.9(2)
134.0(3)
Pt-N(1)-P(1)
Pt-C(1)-P(2)
N(2)-P(2)-C(1)
93.0(2)
132.3(3)
115.4(2)
Ch a r t 1. P u ta tive Electr on Deloca liza tion w ith in
1 for P t(cod )(1-KC,KN) (2)
Carbene complexes bearing coordinated olefins are
particularly important in that they are probably impli-
cated as intermediates in olefin metathesis catalytic
cycles.34 Compound 2 represents a rare example of a
such a Pt-carbene complex. Two other Pt compounds
in this category are the NHC-ethylene complex [PtCl2-
(η2-C2H4)(NHC)]18 (NHC ) 1-ethyl-3-methylimidazol-2-
ylidene), and the five-coordinate Fischer carbene-
ethylene complex [(dmphen)PtCl(CHNMe2)(η2-C2H4)]27
(dmphen ) 2,9-dimethylphenanthroline). To date, the
only examples other than 2 of Pt carbene complexes
bearing a chelating diolefin are the family of hydro-
silylation catalysts supported by a range of NHCs, [Pt-
(η4-O(Me2SiCHdCH2)2)(NHC)].14
the cod ligand of 2 with respect to substitution by
common bases (vide infra).
Assignment of an oxidation state to the Pt center in
2 is complicated in that although simple electron
counting yields 18 electrons and a corresponding oxida-
tion state of 0, the square-planar coordination geometry
of the complex suggests Pt(II). Restricted Hartree-Fock
calculations by Nakamura and Morokuma have found
that the 18-electron carbene carbonyl complex cis-[Pt-
(PH3)2(CO)(CH2)] adopts a square-planar structure as
its most stable coordination geometry, with the C-H
bonds in the plane.33 The stability of the square-planar
structure over a tetrahedral one was attributed to CH2-
(π)-Pt(pπ) overlap, which constitutes the HOMO in this
complex.33 The square-planar geometry of 2 may like-
wise be the result of such an overlap. In light of these
We have examined the reactivity of 2 with a number
of substrates and have found that the complex is
relatively inert under air- and moisture-free conditions.
Contrary to our expectations, treatment of C6D6 solu-
tions of 2 (typically 10 mg) either with 2 equiv of PPh3,
SdPPh3, P(OEt)3 or pyridine or with 1 equiv of 1,1′-bis-
(diphenylphosphino)ferrocene (dppf) or 1,2-bis(diphenyl-
phosphino)ethane (dppe) at room temperature resulted
neither in substitution of the cod ligand nor in opening
of the four-membered C,N-chelate. Heating these solu-
tions to 50-90 °C for periods of 2-5 h resulted in all
cases (except that of dppe, vide infra) in complex
mixtures whose NMR spectroscopic characteristics could
not be reconciled with any of the anticipated substitu-
(33) Nakamura, S.; Morokuma, K. Organometallics 1988, 7, 1904-
1909.
(34) Sanford, M. S.; Love, J . A.; Grubbs, R. H. J . Am. Chem. Soc.
2001, 123, 6543-6554.

2836 Organometallics, Vol. 22, No. 14, 2003
J ones et al.
tion products. No reaction was observed between 2 and
ethylene, nor between 2 and H2 at room temperature
and 1 atm. However, prolonged heating of the H2
reaction mixture in a sealed NMR tube (90 °C, 24 h)
resulted in an orange solution (completely clear to visual
inspection) containing cyclooctane and free H2-1, the
latter representing the only spectroscopically observable
P-containing product. The fate of the Pt in this reaction
remains to be determined. Similarly, heating 2 in the
presence of excess H2SiEt2 also gave H2-1 as the single
P-containing product.
Like those of 2 and 3, the 31P{1H} NMR spectrum of
4 (under 1 atm of CO2) consists of two doublets (δP 17.45
2
2
2
(d, J PP ) 67.2 Hz), 78.38 (d, J PP ) 67.2 Hz, J PPt
)
340 Hz)). The downfield resonance lies in the typical
range for a P atom involved in a four-membered C,N
chelate in these systems (65-80 ppm) and displays the
characteristic two-bond P-Pt coupling (300-550 Hz)
which results from the PdN-Pt linkage (vide supra).
Furthermore, just as the reaction of 2 and MeOTf causes
a dramatic downfield shift of the doublet attributed to
the uncoordinated PdN group of 2 (∆δ ) 33.4), so
reaction with CO2 effects a similar change (∆δ ) 18.6).
Further evidence for the participation of the uncoordi-
nated N atom in the reaction of 2 and CO2 comes from
the fact that 3 does not react with 1 atm of CO2,
presumably on account of the fact that its “dangling”,
methylated N atom is no longer available for nucleo-
philic attack. Evidence for N-to-O migration of the
trimethylsilyl group in the reaction of 2 with CO2 is
Although unreactive toward nucleophiles, complex 2
reacts with strong electrophiles. Thus, treatment of an
ethereal solution of 2 with 1 equiv of MeOSO2CF3
(MeOTf) cleanly affords the canary yellow N-methylated
complex [Pt(η4-cod){dC(Ph2PdNSiMe3)(Ph2PdN(Me)-
SiMe3)-κC,κN}][OTf] (3) which precipitates from solu-
tion. This species can be distinguished easily from the
hypothetical carbene-methylated alternative [Pt(η4-cod)-
{dC(Me)(Ph2PdNSiMe3)2-κC,κN}][OTf] by 1H NMR spec-
troscopy. The NMe protons of 3 give rise to a doublet (δ
derived from 29Si NMR spectroscopy. Given their rela-
2
tive similarities to data for H2-1 (δSi -11.59 (d, J SiP
)
3
3.19, J HP ) 14.4 Hz) arising from coupling to a single
19.2 Hz)),40 the two resonances in 2 (δSi -19.1 (d, SiA,
2J SiP ) 22.3 Hz), 5.2 (dd, SiB, 2J SiP ) 26.1, 4J SiP ) 24.3))
may be assigned as in [Pt(η4-cod){dC(Ph2PdNSiB-
Me3)(Ph2PdNSiAMe3)-κC,κN}], where the italicized ele-
ments represent those that are bound to Pt. (It remains
unclear as to why SiB couples to both P atoms, whereas
SiA couples only to one of them. It is possible that the
four-membered chelate has an effect on the Si-P
coupling similar to the effect it appears to have on the
P-Pt coupling.) It is expected that an N-to-O migration
of the trimethylsilyl group should cause both a marked
effect on the chemical shift of its Si atom and dramati-
cally reduce the Si-P coupling. This is, in fact, exactly
what is observed in the 29Si NMR spectrum of 4, i.e.,
[Pt(η4-cod){dC(Ph2PdNSiCMe3)(Ph2PdNC(O)OSiDMe3)-
κC,κN}] (δSi 21.49 (s, SiC), 13.33 (d, SiD, 2J SiP ) 22.3 Hz))
(Scheme 2).
P atom, not to the doublet of doublets that would result
from a methyl group coupling to two inequivalent P
atoms in the hypothetical product. Other than a ∼30
ppm downfield shift of the 31P resonance attributed to
the dangling PdNSiMe3 “arm” in 2, and the presence
of the doublet at δ 3.19 in the proton spectrum, there
are no significant differences between the NMR spectra
of 2 and 3. This indicates that, aside from methylation
of the uncoordinated N atom, the overall symmetry and
topology of 3 are very similar to that of 2. That is, the
four-membered C,N chelate containing the P-C double
bond is preserved, as is the η4-cod ligand.
The carbene complex 2 reacts in a related manner
with CO2. Treatment of a hexanes suspension of 2 with
1 atm CO2 at room temperature results in a slow orange
to yellow transformation of the slurry. Elemental analy-
sis data of the product are consistent with the formula-
tion of the adduct, 2‚CO2, and on the basis of the
following spectroscopic and experimental evidence, as
well as the knowledge of the higher affinity of Si for O
than for N (799 vs 470 kJ mol-1 bond energies, respec-
tively, for the gaseous diatomic molecules35), we have
formulated this compound as [Pt(η4-cod){dC(Ph2Pd
NSiMe3)(Ph2PdNC(O)OSiMe3)-κC,κN}] (4). The product
results from insertion of CO2 into the N-Si bond via
initial nucleophilic attack on CO2 by the uncoordinated
N atom of 2, followed by trimethylsilyl group migration
from N to O. Such migration is a well-known phenom-
enon. It has been been observed previously by us in
reactions of Me3SiNP(Ph2)CH2PPh2 and ReO3(OSiMe3),36
by Gerlach and Arnold in VO(N(SiMe3)2)2 complexes,37
by Schrock et al. in reactions of CO with Mo and W tri-
(amido)amine complexes,38 and by Veith and co-workers
in the synthesis of polycyclic compounds containing N
and Ge.39
In contrast to our findings, Elsevier and co-workers
observed aza-Wittig reactivity between related com-
plexes and CO2.31 The difference between Elsevier’s
system and ours most probably derives from the absence
in their systems of a N-Si bond. The expected product
of an aza-Wittig reaction between 2 and CO2, TMS-
NdCdO, was not observed in this work.
Early-transition-metal pincer carbene complexes react
with other heteroallenes such as isocyanates (e.g.,
AdNdCdO) and carbodiimides (e.g., Cy2NdCdNCy2) to
form [2 + 2] cycloaddition products in which bonds are
formed between the (more electronegative) heteroatom
and the metal and between the carbene C atom and the
central heteroallene C atom.8 In contrast to this, neither
of the two heteroallenes above react with 2 at room
temperature.
In the absence of added substrates, heating 2 (sealed
tube, benzene, 100 °C, 20 h) results in ortho metalation
of one of the phenyl rings and rearrangement, possibly
through a Pt(IV)-hydride intermediate, to give [(η4-
cod)P t {CH (P h (C6 H 4 )P dN SiMe3 )(P h 2 P dN SiMe3 )-
κC,κC′}] (5). Efforts to observe the intermediate by NMR
spectroscopy have not yet been successful, nor have
attempts to abstract the hydride with [Ph3C][BF4].
(35) Kerr, J . A. In CRC Handbook of Chemistry and Physics: A
Ready Reference of Chemical and Physical Data, 81st ed.; Lide, D. R.,
Ed.; CRC Press: Boca Raton, FL, 2000.
(36) Katti, K. V.; Cavell, R. G. Inorg. Chem. 1989, 28, 3033-3036.
(37) Gerlach, C. P.; Arnold, J . Inorg. Chem. 1996, 35, 5770-5780.
(38) Schrock, R. R.; Rosenberger, C.; Seidel, S. W.; Shih, K.-Y.; Davis,
W. M.; Odom, A. L. J . Organomet. Chem. 2001, 617-618, 495-501.
(39) Veith, M.; Rammo, A.; Hans, M. Phosphorus Sulfur Relat. Elem.
1994, 93, 197-200.
(40) Measured in this work.

An Unusual Platinum Olefin Carbene Complex
Organometallics, Vol. 22, No. 14, 2003 2837
2
2
2J PP ) 5.91 Hz, J PPt ) 200 Hz), 9.27 (d, J PP ) 5.91
2
Hz, J PPt ) 125 Hz)), indicating two chemically in-
equivalent yet similar P atoms, as expected. Both P
atoms in 5 show two-bond coupling to Pt, unlike those
in 2, but the magnitude of this coupling is lower than
for the parent complex. As expected, the 195Pt{1H} NMR
spectrum shows a doublet of doublets (δPt 872) with the
anticipated coupling constants.
The overall symmetry of 5 is lower than that of 2.
1
This is particularly manifest in its H NMR spectrum,
which shows four multiplets (and their associated Pt
satellites) due to the olefinic protons of coordinated cod.
The methine proton of the ortho-metalated ligand gives
rise to a distinctive doublet of doublets (δH 3.88 (dd, 2J PP
) 13.6 Hz, 2J PP ) 16.0 Hz, 2J PPt ) 96 Hz)). The presence
of diastereomers, which would be manifest in a complete
1
second set of peaks, was not observed in either the H
or the 31P{1H} solution NMR spectra of 5.
The transformation of 2 to 5 requires an ortho
metalation, a 1,2-H shift, and dissociation of the bound
N atom. Although the ordering of these steps is uncer-
tain, it is likely to be one of the phenyl rings associated
with a “dangling” rather than with a bound Ph2Pd
NSiMe3 group that undergoes the metalation reaction:
rotation about the P-C(carbene) bond of the former
group would bring the ortho phenyl C atoms close to
the Pt center. The crystal structure of 2 reveals, on the
other hand, that the Pt-C(ortho phenyl) distances for
the bound (endocyclic) Ph2PdNSiMe3 group are 4.158
and 4.401 Å, probably too distant for metalation without
dissociation of the N atom.
F igu r e 2. ORTEP representation (20% ellipsoids) of the
molecular structure of 5. For every phenyl ring except the
ortho-metalated one, only the ipso carbon atom is shown.
Except for H(1), the hydrogen atoms have been omitted for
clarity.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5 w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
Pt-C(1)
Pt-C(2)
Pt-C(6)
P(1)-C(1)
P(2)-C(1)
2.098(6)
2.202(6)
2.265(5)
1.822(6)
1.805(6)
Pt-C(12)
Pt-C(3)
2.029(5)
2.201(6)
2.255(5)
1.535(5)
1.546(5)
Pt-C(7)
P(1)-N(1)
P(2)-N(2)
Without saying whether dissociation of the coordi-
nated N atom occurs before or after the ortho-metalation
event, we lean toward an oxidative addition, or nucleo-
philic, pathway for the cyclometalation reaction, even
though we have been unable to detect a Pt-hydride
intermediate. This is because the ortho metalation
proceeds diasteroselectively, generating two stereo-
centers whose relative absolute configurations are fixed.
Thus, if the absolute configuration at the stereogenic P
atom in 5 is R, the configuration at the formerly carbene
C atom will also be R, and vice versa. This is consistent
with the two degenerate oxidative addition pathways
shown in Scheme 3. Hydride I, which results from an
anticlockwise rotation about the P-C(carbene) bond, is
R at P and will give rise to R,R-5 by proton transfer
from Pt to the carbene C atom. Conversely, hydride II,
which results from clockwise rotation, is S at P and will
give rise to S,S-5. If the mechanism were electrophilic,
and H+ rather than coordinated hydride resulted from
the C-H activation, it would seem unlikely, even with
the participation of the available N bases in 2, that the
carbene C atom would be protonated with perfect facial
selectivity. This observation is in accord with the idea
that C-H activations at Pt(II) typically proceed by
nucleophilic pathways.41
C(1)-Pt-C(12)
P(1)-C(1)-P(2)
N(2)-P(2)-C(1)
85.2(2)
119.7(3)
112.0(3)
N(1)-P(1)-C(1)
C(1)-P(1)-C(11)
Pt-C(1)-P(1)
118.0(3)
99.0(3)
103.9(3)
An ORTEP representation of the molecular structure
of 5 is shown in Figure 2; selected bond lengths and
angles appear in Table 2. The coordination environment
is essentially square planar, as expected, but in this case
the bond lengths and angles are typical for Pt-alkyls
and Pt-arenes. In addition, 5 does not display the kind
of charge delocalization found in 2. Thus, the P-C(H)
bonds in 5 (average 1.814(6) Å) are similar to those
found in H2-1 (1.827(1) Å), as are the PdN lengths
(average 1.541(5) vs 1.539(2) Å for H2-1). The bond
distances between Pt and the olefinic C atoms trans to
C(H) (C(2) and C(3), average 2.201(6) Å) in 5 are more
similar to those found trans to C(carbene) in 2 (average
2.212(5) Å) than to those between Pt and the other
olefinic C atoms, i.e., trans to C(phenyl), which are
considerably longer (C(6) and C(7), average 2.600(5) Å).
The ortho-metalated complex 5 posseses two stereo-
genic centers, C(1) and P(1). Shown in Figure 2 is the
S,S enantiomer; because the space group of this struc-
ture is centrosymmetic (P21/n), the opposite enatiomer
is also present in equal abundance in the unit cell.
Absent, however, are the R,S diastereomers. These
observations, together with solution NMR data (vide
infra), are consistent with diastereoselective formation
of 5.
Coordinative unsaturation in square-planar com-
plexes is known to be an important prerequisite for
cyclometalation, as has been demonstrated by White-
sides and co-workers in C-H activation reactions
involving bis(neopentyl) complexes of Pt(II).42 It is
The 31P{1H} NMR spectrum of 5 shows the solution
structure of the complex to be consistent with the solid-
state structure. It consists of two closely separated
doublets and their associated Pt satellites (δP 9.61 (d,
(41) Ryabov, A. D. Chem. Rev. 1990, 90, 403-424.
(42) Foley, P.; DiCosimo, R.; Whitesides, G. M. J . Am. Chem. Soc.
1980, 102, 6713-6725.

2838 Organometallics, Vol. 22, No. 14, 2003
J ones et al.
Sch em e 3. Degen er a tive Oxid a tive Ad d ition ,
Hyd r id e Tr a n sfer P a th w a ys in th e Tr a n sfor m a tion
of 2 to 5
phenomenon to the thermodynamic requirement for
eliminated HCl to be ionized, but because there is no
such elimination in our case, this rationale cannot be
applied here. The dependence of rate of cyclometalation
reactions on solvent has also been observed by Simpson
and co-workers in the reactions of cis-[PtCl2(dmso)2] and
tertiary ferrocenylamines in CHCl3 or acetone vs MeOH
or H2O.44
In our case, it seems possible that H2O may increase
the propensity for dissociation of the bound N atom in
2 by competing for the coordination sphere of the metal,
while it itself remains only weakly bound. This may
accelerate the ortho-metalation process by increasing
the concentration of coordinatively unsaturated Pt
centers. Further exploration of this system is currently
under way.
Although 2 does not react with dppe at room temper-
ature, heating a benzene solution of the two compounds
to 100 °C for several hours results in the slow consump-
tion of 2 to give, not the expected product [Pt(dppe)-
{dC(Ph2PdNSiMe3)2-κC,κN}], but rather the ortho-
metalated complex [Pt(dppe){CH(Ph(C6H4)PdNSiMe3)-
(Ph2PdNSiMe3)-κC,κC′}] (6). This must result from slow
formation of 5, which subsequently reacts quickly with
dppe to form 6. Indeed, periodic monitoring of the high-
temperature reaction between 2 and dppe by NMR
spectroscopy (at room temperature) does not reveal 5
but instead shows unreacted 2 and the final product 6.
This product is characterized by four chemically in-
equivalent P atoms, two of which show the anticipated
single-bond P-Pt coupling and two of which show two-
bond coupling. Complex 6 can also be made rationally,
of course, by reacting isolated 5 with a stoichiometric
quantity of dppe.
When the reaction between [Li2-1]2 and [PtCl2(η4-cod)]
was conducted in C6H6 as opposed to Et2O, a very
different product from 2, [Li][Pt{CH(Ph(C6H4)Pd
NSiMe3)(Ph2PdNSiMe3)-κC,κC′}{CH(Ph2PdNSiMe3)2-
κC,κN}] (7), was isolated in low yield. This complex may
be thought of as the product of the reaction between 5
and LiH-1, in which [H-1]- forms a four-membered C,N
chelate with the metal center and the overall negative
charge on the Pt complex is balanced by Li+, which
remains coordinated to three of the four N atoms
(Scheme 2).
An ORTEP representation of the molecular structure
of 7 is shown in Figure 3; selected bond distances and
angles are given in Table 3. The Pt-C(1) and Pt-C(12)
bond lengths in 7 are almost exactly the same as the
corresponding distances in 5.
In contrast to the reaction between [Li2-1]2 and [PtCl2-
(η4-cod)] in Et2O solution, in which the deep orange color
of the product, 2, begins to form within minutes, the
corresponding reaction in C6H6 is slow. Indeed, in situ
NMR spectroscopic analysis of the reaction mixture
after 2 h at room temperature reveals no formation of
2. After 20 h, both 2 and 5 are apparent, in addition to
unreacted [Li2-1]2 and traces of H2-1. After this mixture
had been stirred at room temperature for a total of 5
days and then heated to 100 °C for 20 h, a 22% yield of
7 was recovered after recrystallization (see Experimen-
tal Section).
possible that in our case the rate-limiting step in the
conversion of 2 to 5 is dissociation of the coordinated N
atom; the fact that NMR measurements show that the
N atoms of 2 are not in chemical exchange is consistent
with the hypothesis that the coordinated N atom is
tightly bound, as is the fact that the C,N chelate of 2 is
not opened by a variety of reagents (vide supra).
Following dissociation, oxidative addition to the three-
coordinate intermediate gives a Pt hydride which rap-
idly decomposes to 5.
The transformation of 2 to 5 is promoted by adventi-
tious water. Heating of a very dry C6D6 solution of 2 to
60 °C for 14 h gave no conversion to 5, as determined
by NMR spectroscopy. However, in the presence of 5
equiv of H2O, conversion was complete within 10 min
at this temperature. It is possible that slow transforma-
tion at higher temperature (100 °C) results either from
water that becomes available via desorption from glass
surfaces or through a thermal route in which water is
not involved.
The accelerating effect of water on ortho-metalation
reactions has been observed previously by Rourke and
co-workers.43 These researchers observed that the rate
of the second cycloplatination of 2,6-diphenylpyridine
in [{(o-C6H4)py(o-C6H5)-κC,κN}PtCl(CO)] was enhanced
by addition of water or base. They attributed this
(43) Cave, G. W. V.; Fanizzi, F. P.; Deeth, R. J .; Errington, W.;
Rourke, J . P. Organometallics 2000, 13, 500-510.
(44) Ranatunge-Bandarage, P. R. R.; Robinson, B. H.; Simpson, J .
Organometallics 1994, 13, 500-510.

An Unusual Platinum Olefin Carbene Complex
Organometallics, Vol. 22, No. 14, 2003 2839
distances in this complex are indicative of an electron-
rich Pt center. Correspondingly, the low nucleophilicity
of the carbene C atom is consistent with its electron
deficiency. We believe that the carbene complex 2 may
be an example of a square-planar 18-electron Pt(II)
metal center bonded to 12-. In contrast, the ortho-
metalated complex 5 behaves typically for 16-electron
Pt(II) complexes; its cod ligand is readily substituted
by chelating phosphines in the usual fashion. Investiga-
tion into the use of 2 and 5 in other reactions is
currently under way.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed either in an Ar-filled glovebox or under an Ar or N2
atmosphere using standard Schlenk techniques. Solvents were
dried over appropriate drying agents and degassed by three
freeze-pump-thaw cycles prior to use. The organolithium
compounds [Li2-1]21 and LiH-145 were prepared according to a
minor modification of our published procedures. The precursor
[PtCl2(cod)] was made by the method of Whitesides and co-
workers;46 other transition-metal precursors were purchased
from commercial sources. Unless otherwise indicated, NMR
spectra were recorded at ambient temperature using C6D6
solutions of the complexes on a Varian i400 spectrometer
(161.9 MHz for 31P, 100.6 MHz for 13C, 79.5 MHz for 29Si, 85.7
MHz for 195Pt) and referenced to residual solvent proton (1H),
solvent carbon (13C), external TMS (29Si: δ 0.00), external
P(OMe)3 (31P, δ 141.00 vs external 85% H3PO4), or external
10% aqueous H2PtCl6 (195Pt, δ 4522). All J values are given in
Hz; abbreviations used are s ) singlet, d ) doublet, t ) triplet,
m ) multiplet, and p ) pseudo. Elemental analyses were
performed by Ms. Darlene Mahlow of the University of Alberta
Chemistry Department. IR spectra were recorded using KBr
pellets on a Bomem MB100 instrument and are reported in
cm-1; abbreviations used are s ) strong, m ) medium, and w
) weak.
F igu r e 3. ORTEP representation (20% ellipsoids) of the
molecular structure of 7. For every phenyl ring except the
ortho-metalated one, only the ipso carbon atom is shown.
Except for H(1) and H(2), the hydrogen atoms have been
omitted for clarity.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 7 w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
Pt-C(1)
Pt-C(2)
Li-N(2)
Li-N(4)
2.091(7)
2.155(7)
2.073(16)
2.074(16)
Pt-C(12)
Pt-N(3)
Li-N(3)
2.000(8)
2.256(6)
2.212(16)
C(1)-Pt-C(12)
C(1)-Pt-C(2)
N(2)-Li-N(3)
N(2)-Li-N(4)
86.0(3)
N(3)-Pt-C(2)
N(3)-Pt-C(12)
N(3)-Li-N(4)
73.4(2)
168.8(3)
105.6(7)
171.1(3)
111.4(7)
141.9(8)
The product distribution after 20 h is likely due (i) to
the presence of adventitious water, which both promotes
the ortho metalation of 2 and also reacts with [Li2-1]2
to give H2-1, and (ii) to the fact that the reaction betwen
[Li2-1]2 and [PtCl2(η4-cod)] in benzene is sluggish,
presumably on account of the stability of the fomer
cluster in donor-free solvent, and the conversion of 2 to
5 therefore occurs at a rate comparable to the formation
of 2. The resulting simultaneous presence of both 5 and
[Li2-1]2 in the reaction mixture is the condition that
ultimately must give rise to the formation of 7. The
methanide LiH-1, which is formed, presumably, either
by partial hydrolysis of [Li2-1]2 or by disproportionation
of [Li2-1]2 and H2-1, reacts with 5 to give 7. This is
consistent with our observation that the cod ligand of 5
is substitutionally labile, whereas that of 2 is not. To
confirm these hypotheses, the reaction between isolated
5 and LiH-1 was performed and followed in situ by NMR
spectroscopy; it did indeed give 7.
Syn th eses. [P t(η4-cod ){dC[P h 2P dNSiMe3]2-KC,KN}] (2).
To an Et2O suspension (35 mL) of [Li2-1]2 (0.86 g, 0.75 mmol)
was added [PtCl2(cod)] (0.55 g, 1.5 mmol) as a solid in a single
portion at room temperature. The resulting milky yellow
suspension was stirred at room temperature for a period of
24 h, over which time the mixture turned a deep red. The solids
were removed by centrifugation, and the red organic portion
was reduced in vacuo to approximately 5 mL. This mixture
was cooled to -18 °C overnight, and red crystals (0.27 g) of 2
formed. The supernatant was decanted, further reduced, and
cooled again to obtain a second crop (0.27 g) of 2. Repeating
this procedure allowed for the isolation of further two portions
of 2 (combined weight 0.083 g); the overall yield of 2 was 0.62
g (49%). In the solid state, 2 is stable to air for short periods
of time. Anal. Calcd for C39H50N2P2PtSi2: C, 54.5; H, 5.9; N,
1
3.3. Found: C, 54.1; H, 5.9; N, 3.3. H NMR: δ -0.01 (s, 9H,
Si(CH3)3), 0.48 (s, 9H, Si(CH3)3), 1.53 (m, 4H, cod CH2), 2.03
2
Con clu sion
(m, 4H, cod CH2), 4.93 (m, 2H, cod CH, J HPt ) 48), 5.88 (m,
2
2H, cod CH, J HPt ) 72), 7.03 (m, 6H, Ph H), 7.16 (m, 8H, Ph
In all our previous investigations, we have found the
formally dianionic ligand 1 to coordinate through its
carbene C atom as well as both N atoms, either as a
“pincer” or a bridging carbene, and the question has
arisen as to whether the N donors were necessary to
stabilize the complexes. In the case of 2, we have now
shown that only one coordinated N atom is necessary
in the case of Pt. Indeed, the reactivity of 2 is dominated
by the uncoordinated N atom; reactions with electro-
philes demonstrate that this center is more nucleophilic
than the carbene C atom. The substitutional inertness
of the cod ligand in 2 and the short Pt-C(olefin)
H), 7.81 (m, 8H, Ph H). 13C{1H} NMR: δ 4.3 (d, Si(CH3)3, 3J CP
3
) 3.3), 5.1 (d, Si(CH3)3, J CP ) 2.6), 29.5 (s, cod CH2), 31.7 (s,
1
1
cod CH2), 49.2 (dd, PCP, J CP ) 134, J CP ) 84), 84.7 (s, cod
1
1
CH, J CPt ) 167), 91.4 (s, cod CH, J CPt ) 84), 127.2-132.7
(m, Ph C), 138.0-143.8 (m, Ph C). 31P{1H} NMR: δ -1.1 (d,
2J PP ) 67, J PPt ) 0), 65.5 (d, J PP ) 67, J PPt ) 530). 29Si{1H}
2
2
2
2
2
NMR (toluene-d8): δ -19.1 (d, J SiP ) 22), 5.2 (dd, J SiP ) 26,
4J SiP ) 24). 195Pt{1H} NMR: δ 1136 (d, J PtP ) 520). Crystals
2
(45) Babu, R. P. K.; Aparna, K.; McDonald, R.; Cavell, R. G.
Organometallics 2001, 20, 1451-1455.
(46) McDermott, J . X.; White, J . F.; Whitesides, G. M. J . Am. Chem.
Soc. 1976, 98, 6521-6528.

2840 Organometallics, Vol. 22, No. 14, 2003
J ones et al.
Ta ble 4. Cr ysta llogr a p h ic Da ta for 2, 5, a n d 7 w ith Estim a ted Sta n d a r d Devia tion s in P a r en th eses
2
5
7
A. Crystal Data
39H50N2P2PtSi2
860.02
mol formula
mol wt
C
C39H50N2P2PtSi2
860.02
C62H77LiN4P4PtSi4
1316.55
cryst dimens (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.25 × 0.15 × 0.15
orthorhombic
Pbca (No. 61)
18.840(3)
24.212(4)
16.866(3)
90
90
90
7693(2)
8
1.485
0.32 × 0.18 × 0.06
monoclinic
P21/n (No. 14)
11.1730(12)
20.393(2)
16.7965(18)
90
97.709(2)
90
3792.5(7)
4
0.25 × 0.08 × 0.05
monoclinic
P21/n (No. 14)
14.5678(16)
23.722(3)
18.762(2)
90
98.823(2)
90
6407.1(12)
4
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
F
calcd (g cm-3
)
1.506
3.877
1.365
2.405
µ (mm-1
)
3.822
B. Data Collection and Refinement
diffractometer
radiation (λ (Å))
temp (K)
Bruker PLATFORM/SMART 1000 CCD
graphite-monochromated Mo KR (0.710 73)
193
total no. of data collected
index ranges
48 592
22 819
39 411
-23 e h e 23
-30 e k e 30
-19 e l e 21
7910 (0.1139)
7910/0/415
0.920
0.0385
0.0943
2.876 and -1.761
-13 e h e 13
-24 e k e 25
-20 e l e 20
7701 (0.0754)
7701/0/415
1.001
0.0408
0.0881
2.592 and -0.693
-18 e h e 18
-29 e k e 28
-23 e l e 23
13059 (0.1668)
13059/0/680
0.938
0.0567
0.1174
1.988 and -0.710
no. of indep rflns (Rint
)
2
no. of data (Fo g -3σ(Fo2))/restraints/params
goodness of fit (Sa) (Fo g -3σ(Fo2))
2
b
2
R1 (Fo g 2σ(Fo2))
wR2c (Fo g -3σ(Fo2))
2
largest diff peak and hole (e Å-3
)
S ) [∑w(Fo - Fc2)2/(n - p)]1/2 (n ) number of data; p ) number of parameters varied; w ) [σ2(Fo2) + (A0P)2]-1 where P ) [Max(Fo
,
a
2
2
0) + 2Fc2]/3) and A0 ) 0.0481 (2), 0.0356 (5), 0.0354 (7). R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) [∑w(Fo - Fc2)2/∑w(Fo4)]1/2
.
b
2
2
2
2
suitable for X-ray diffraction analysis were obtained directly
from the initial crop of 2.
) 67, J PPt ) 0), 78.4 (br d, J PP ) 67 Hz, J PPt ) 340). 29Si
2
NMR (toluene-d8): δ 21.5 (s, OSi), 13.3 (d, NSi, J SiP ) 22).
[P t (η4-cod ){dC(P h 2P dN(Me)SiMe3)(P h 2P dNSiMe3)}-
KC,KN}][OTf] (3). To an orange Et2O (4 mL) solution contain-
ing 2 (0.076 g, 0.088 mmol) was added neat MeOTf (10.5 µL,
0.093 mmol) in a single portion by microliter syringe. Within
seconds, a canary yellow precipitate formed. This was isolated
by centrigugation, washed with Et2O (2 × 3 mL), and dried in
vacuo. Yield: 0.064 g (71%). Anal. Calcd for C41H53N2F3O3P2-
PtSSi2: C, 48.1; H, 5.2; N, 2.7. Found: C, 47.9; H, 5.4; N, 2.6.
1H NMR (THF-d8): δ -0.17 (s, 9H, Si(CH3)3), -0.10 (s, 9H,
Si(CH3)3), 2.15 (m, 4H, cod CH2), 2.37 (m, 2H, cod CH2), 2.53
[P t (η4-cod ){CH (P h (C6H 4)P dNSiMe3)(P h 2P dNSiMe3)-
KC,KC′}] (5). A C6D6 solution of 2 (0.091 g, 0.106 mmol) was
sealed in an NMR tube that was subsequently immersed in a
100 °C oil bath for 20 h. The solvent was then removed in
vacuo to give a pale yellow free-flowing powder that was
recrystallized from Et2O. Yield: 0.069 g (76%). Anal. Calcd
for C39H50N2P2PtSi2: C, 54.5; H, 5.9; N, 3.3. Found: C, 54.1;
1
H, 5.9; N, 3.1. H NMR: δ 0.18 (s, 9H, Si(CH3)3), 0.22 (s, 9H,
Si(CH3)3), 1.00 (m, 1H, cod CH2), 1.16 (m, 1H, cod CH2), 1.36
(m, 2H, cod CH2), 1.54 (m, 1H, cod CH2), 1.95 (m, 1H, cod CH2),
2.10 (m, 1H, cod CH2), 2.61 (m, 1H, cod CH2), 4.00 (dd, 1H,
PCHP, 2J HP ) 13, 2J HP ) 16, 2J HPt ) 96), 4.20 (m, 1H, cod CH,
2J HPt ) 38), 4.45 (m, 1H, cod CH, 2J HPt ) 48), 4.70 (m, 1H, cod
3
(m, 2H, cod CH2), 3.19 (d, 3H, NCH3, J HP ) 14), 4.34 (m, 2H,
2
2
cod CH, J HPt ) 58), 5.54 (m, 2H, cod CH, J HPt ) 42), 7.30-
7.65 (m, 20H, Ph H). 13C{1H} NMR (THF-d8): δ -0.8 (s, Si-
(CH3)3), 2.9 (d, Si(CH3)3, 3J CP ) 3.5), 28.3 (s, cod CH2), 30.5 (s,
cod CH2), 31.0 (s, NCH3), 86.8 (s, cod CH, 1J CPt ) 160), 97.6 (s,
2
2
CH, J HPt ) 48), 6.68 (m, 1H, cod CH, J HPt ) 36), 6.80-8.25
(m, 19H, Ph H). 13C{1H} NMR: δ 4.4 (d, Si(CH3)3, 3J CP ) 2.9),
1
cod CH, J CPt not observed), 128-132 (m, Ph C, Ph CH). The
4.6 (d, Si(CH3)3, 3J CP ) 3.4), 27.9 (s, cod CH2), 28.3 (s, cod CH2),
carbene C atom was not observed. 31P{1H} NMR (THF-d8): δ
30.3 (s, cod CH2), 30.7 (s, cod CH2), 51.3 (dd, Pt-CH, J CP
)
1
2
2
2
2
1
1
33.3 (d, J PP ) 63, J PPt ) 0), 68.6 (d, J PP ) 63, J PPt ) 510).
57, J CP ) 67), 96.4 (s, cod CH, J CPt ) 97), 98.4 (s, cod CH,
1J CPt ) 97), 106.6 (s, cod CH, J CPt ) 42), 106.8 (s, cod CH,
1
[P t(η4-cod ){dC(P h 2P dNSiMe3)(P h 2P dNC(O)OSiMe3)}-
KC,KN}] (4). An orange slurry of 2 (0.035 g, 0.041 mmol) in
hexanes (5 mL) in a round-bottomed flask capped with a
Kontes valve was degassed by two freeze-pump-thaw cycles,
and then 1 atm of CO2 gas was admitted. After 0.5 h of stirring,
the suspension had changed color from orange to yellow. The
yellow solid was isolated by centrifugation and dried in vacuo.
Yield: 0.030 g (82%). Anal. Calcd for C40H50N2O2P2PtSi2: C,
1J CPt ) 48), 125-134 (m, Ph C and Ph CH). 31P{1H} NMR (CD2-
2
2
2
2
Cl2): δ 9.6 (d, J PP ) 5.9, J PPt ) 200), 9.3 (d, J PP ) 5.9, J PPt
) 130). 195Pt{1H} NMR: δ 872 (dd, J PtP ) 130, J PtP ) 200).
Crystals suitable for X-ray diffraction were grown at -18 °C
from a THF solution of 5 that had been layered with hexanes.
2
2
[P t (d p p e ){CH (P h (C6H 4)P dNSiMe 3)(P h 2P dNSiMe 3)-
KC,KC′}] (6). To a combination of 5 (0.090 g, 0.105 mmol) and
dppe (0.042 g, 0.105 mmol) was added C6H6 (3 mL), and the
pale yellow solution was stirred for 3 h. The volume of the
solution was reduced to ca. 0.5 mL in vacuo, and hexanes (10
mL) was added to give an off-white precipitate that was
separated from the solution by centrifugation. The solution
was placed in a -18 °C refrigerator for several days, and a
pale yellow precipitate deposited. The supernatant liquid was
removed, and the solid was dried in vacuo. Yield: 0.050 g
(43%). Anal. Calcd for C57H64N2P4PtSi2: C, 59.4; H, 5.6; N, 2.4.
1
53.1; H, 5.6; N, 3.1. Found: C, 52.7; H, 5.4; N, 3.0. H NMR
(under 1 atm of CO2): δ 0.02 (s, 9H, Si(CH3)3), 0.52 (s, 9H,
Si(CH3)3), 1.42 (m, 4H, cod CH2), 1.82 (br m, 4H, cod CH2),
2
5.72 (br m, 4H, cod CH, J HPt ) 56), 6.90 (m, 6H, Ph H), 7.05
(m, 6H, Ph H), 7.95 (m, 8H, Ph H). 13C{1H} NMR: δ -0.1 (s,
Si(CH3)3), 1.2 (s, Si(CH3)3), 29.1 (s, cod CH2), 31.6 (s, cod CH2),
88.3 (s, cod CH), 96.7 (s, cod CH), 127-134 (m, Ph CH), 137.6
(d, Ph C, 1J CP ) 100). The PCP and NC(O)O C atoms were not
2
observed. 31P{1H} NMR (under 1 atm of CO2): δ 17.5 (d, J PP

An Unusual Platinum Olefin Carbene Complex
Organometallics, Vol. 22, No. 14, 2003 2841
1
Found: C, 59.8; H, 5.7; N, 2.4. H NMR: δ -0.12 (s, 9H, Si-
refinement of the setting angles of 7006 (2), 7635 (5), and 4139
(7) reflections from the data collection. The space groups were
determined to be Pbca (No. 61), P21/n (No. 14), and P21/n (No.
14), respectively. The data were corrected for absorption
through use of a multiscan procedure (SADABS).
2
2
(CH3)3, J HSi ) 6), 0.04 (s, 9H, Si(CH3)3, J HSi ) 6), 1.04 (m,
1H, CH2), 1.43 (m, 1H, CH2), 1.64 (m, 1H, CH2), 1.73 (m, 1H,
2
CH2), 4.15 (m, 1H, Pt-CH, J HPt ) 85), 6.54-8.10 (m, 20H,
Ph H). 13C{1H} NMR: δ 4.5 (d, Si(CH3)3, J CP ) 2.9), 4.6 (d,
3
Si(CH3)3, 3J CP ) 3.8), 23.0 (s, CH2), 31.9 (s, CH2), 124-136 (m,
The structures of 2, 5, and 7 were solved using automated
Patterson location of the heavy metal atoms and structure
expansion using the DIRDIF-9648 program. Refinement was
completed using the program SHELXL-93.49 Hydrogen atoms
were assigned positions based on the geometries of their
attached carbon atoms and were given thermal parameters
20% greater than those of the attached carbons. The final
model for 2 was refined to values of R1(F) ) 0.0385 (for 5439
Ph C and Ph CH). 31P{1H} NMR: δ 14.41 (d,
J
) 13, J PPt
2/3
2
PP
2
2
2
) 100), 15.39 (dd, J PP ) 10, J PP ) 31, J PPt ) 160), 41.05
(appears as a pt, but must be a dd with two almost identical
2/3
coupling constants:
J
≈ 13, 2/3J PP ≈ 13, 1J PPt ) 2670), 43.70
PP
2
1
(d, J PP ) 31, J PPt ) 1800).
[Li][P t{CH(P h (C6H4)P dNSiMe3)(P h 2P dNSiMe3)-KC,KC′}-
{CH(P h 2P dNSiMe3)2-KC,KN}] (7). To a combination of [PtCl2-
(cod)] (0.17 g, 0.46 mmol) and [Li2-1]2 (0.26 g, 0.23 mmol) was
added C6H6 (20 mL) to give a yellow solution that was stirred
at ambient temperature for 5 days and then at 100 °C for 20
h. The solvent was removed in vacuo to give an oily brown
residue that was extracted with hexanes (2 × 10 mL). The
combined extracts were concentrated and cooled to -20 °C.
Colorless X-ray diffraction quality crystals deposited. The
supernatant liquid was decanted, and the crystals were
washed with precooled hexanes and dried under vacuum.
Yield: 0.078 g (26%). Anal. Calcd for C62H77N4LiP4PtSi4: C,
data with Fo g 2σ(Fo2)) and wR2(F2) ) 0.0943 (for all 7910
2
independent data), that of 5 was refined to values of R1(F) )
0.0408 (for 5356 data with Fo2 g 2σ(Fo2)) and wR2(F2) ) 0.0881
(for all 7701 independent data), and finally that of 7 was
2
refined to R1(F) ) 0.0567 (for 7482 data with Fo g 2σ(Fo2))
and wR2(F2) ) 0.1174 (for all independent data).
Ack n ow led gm en t. We thank Dr. J ames Dennett for
useful discussions. The Natural Sciences and Engineer-
ing Research Council of Canada (NSERC), the Univer-
sity of Alberta, the donors of the Petroleum Research
Fund (administered by the American Chemical Society),
and the Izaak Walton Killam Foundation are gratefully
acknowledged for financial support of this work.
1
56.6; H, 5.9; N, 4.3. Found: C, 55.7; H, 6.0; N, 4.0. H NMR:
δ -0.18 (s, 9H, Si(CH3)3), 0.25 (s, 9H, Si(CH3)3), 0.31 (s, 9H,
Si(CH3)3), 0.44 (s, 9H, Si(CH3)3), 2.36 (m, 1H, PCHP), 4.38 (dd,
2
2
1H, PCHP, J HP ) 20, J HP ) 16), 6.42-9.42 (m, 39H, Ph H).
13C NMR (CD2Cl2): δ 3.9 (d, Si(CH3)3, J CP ) 2.4), 4.5 (d, Si-
3
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data for 2, 5, and 7; these data are also available
as CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
2
(CH3)3, J CP ) 4.5), 5.0 (d, Si(CH3)3, J CP ) 4.1), 5.4 (d, Si-
2
1
1
(CH3)3, J CP ) 4.4), 15.0 (dd, Pt-CH, J CP ) 50, J CP ) 80),
122-146 (m, Ph C, Ph CH). 31P{1H} NMR (CD2Cl2): δ 16.4 (s,
2J PPt ) 160), 22.9 (m, J PPt ) 76), 24.8 (d, J PP ) 5.0, J PPt
)
2
2
2
2
2
OM030003V
100), 30.2 (d, J PP ) 5.0, J PPt ) 270).
Cr ysta llogr a p h y. A summary of crystallographic data for
2, 5, and 7 appears in Table 4. Details are given in the
Supporting Information. Crystals of the three complexes were
grown as outlined in their respective synthetic sections. In all
cases, data were collected on a Bruker PLATFORM/SMART
1000 CCD diffractometer47 using Mo KR radiation at 193 K.
Unit cell parameters were obtained from a least-squares
(47) Programs for diffractometer operation, data collection, data
reduction, and absorption correction were those supplied by Bruker.
(48) Beurskens, P. T.; Beurskens, G.; Bosman, W. P.; Gelder, R. D.;
Granda, S. G.; Gould, R. O.; Israel, R.; Smits, J . M. M. The DIRDIF-
96 Program System; Crystallography Laboratory, University of
Nijmegen, Nijmegen, The Netherlands, 1996.
(49) Sheldrick, G. M. SHELXL-93 Program for Crystal Structure
Determination, University of Go¨ttingen, Go¨ttingen, Germany, 1993.