Reactions of (chloromethyl)platinum(II) derivatives with nucleophiles. Formation of (dimethylamino)carbene complexes using N,N,N′,N′-tetramethylmethanediamine as nucleophile and the X-ray crystal and molecular structures of cis-[(Ph3P)Pt(CH2NMe3)Cl2]

Article abstract of DOI:10.1021/om990049h

Reaction, in chloroform solution, of (COD)Pt(CH₂Cl)Cl (5) with Me₂NCH₂NMe₂ in the presence of 1 equiv (vs 5) of a monodentate ligand L (L = Ph₃P, (p-MeOC₆H₄)₃P, (p-FC₆H₄)₃P, Et₃P, Ph₃As) gives the (dimethylamino)carbene complexes cis-[LPt(CHNMe₂)Cl₂] (1a-e) via the cyclic ylide intermediates [LPt(CH₂NMe₂CH₂NMe₂)Cl]Cl (2a-e). Major byproducts of the reaction are the (trimethylammonio)methyl ylide complexes cis-[LPt(CH₂NMe₃)Cl₂] (11a-e). With L = Ph₃As, carbene product 1e is accompanied by a second carbene complex, trans(As,CH₂)-[(Ph₃As)Pt(CHNMe₂)(CH ₂NHMe₂)Cl]Cl (25). When the reaction with L = Ph₃P is carried out in acetonitrile, the amide chelate [(Ph₃P)Pt(CH₂CH₂CONMe₂)Cl] (24) is formed in addition to 1a and 11a. A deuterium labeling experiment indicates that formation of 24 involves condensation of a CH₂Cl (or derived) moiety with a molecule of solvent. The structures of complexes 11a and 24, and of the hexafluorophosphate analogue (26) of complex 25, have been confirmed by X-ray crystallographic analyses. Carbene complex 1a, along with other products, is also obtained upon reaction of 5 and Ph₃P (1:1) with dimethylamine. Formation of 1a in this case can proceed via two pathways, one involving cyclic ylide species 2a as intermediate and the other the N-protonated (dimethylamino)methyl complex cis-[(Ph₃P)Pt(CH₂NHMe₂)Cl₂] (20). The mechanistic pathways involved in formation of carbene complexes 1a-e and 25, ylide complexes 2a-e and 11a-e, and (dimethylamino)methyl complex 20 are discussed. It is suggested that formation of the ylide complexes and 20 proceeds via initial attack of amine at platinum and that carbene formation proceeds via platinum(IV) carbene hydride intermediates.

Full text of DOI:10.1021/om990049h

2428
Organometallics 1999, 18, 2428-2439
Rea ction s of (Ch lor om eth yl)p la tin u m (II) Der iva tives
w ith Nu cleop h iles. F or m a tion of
(Dim eth yla m in o)ca r ben e Com p lexes Usin g
N,N,N′,N′-Tetr a m eth ylm eth a n ed ia m in e a s Nu cleop h ile
a n d th e X-r a y Cr ysta l a n d Molecu la r Str u ctu r es of
cis-[(P h 3P )P t(CH2NMe3)Cl2],
cis(C,P )-[(P h 3P )P t(CH2CH2C(O)NMe2)Cl], a n d
tr a n s(As,CH2)-[(P h 3As)P t(CHNMe2)(CH2NHMe2)Cl]P F 6
George Ferguson, Yiwei Li, Alan J . McAlees, Robert McCrindle,* and Ke Xiang
Guelph-Waterloo Centre for Graduate Work in Chemistry, Guelph Campus, Department of
Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1
Received J anuary 26, 1999
Reaction, in chloroform solution, of (COD)Pt(CH2Cl)Cl (5) with Me2NCH2NMe2 in the
presence of 1 equiv (vs 5) of a monodentate ligand L (L ) Ph3P, (p-MeOC6H4)3P, (p-FC6H4)3P,
Et3P, Ph3As) gives the (dimethylamino)carbene complexes cis-[LPt(CHNMe2)Cl2] (1a -e) via
the cyclic ylide intermediates [LPt(CH2NMe2CH2NMe2)Cl]Cl (2a -e). Major byproducts of
the reaction are the (trimethylammonio)methyl ylide complexes cis-[LPt(CH2NMe3)Cl2] (11a -
e). With L ) Ph3As, carbene product 1e is accompanied by a second carbene complex,
trans(As,CH2)-[(Ph3As)Pt(CHNMe2)(CH2NHMe2)Cl]Cl (25). When the reaction with L ) Ph3P
is carried out in acetonitrile, the amide chelate [(Ph3P)Pt(CH2CH2CONMe2)Cl] (24) is formed
in addition to 1a and 11a . A deuterium labeling experiment indicates that formation of 24
involves condensation of a CH2Cl (or derived) moiety with a molecule of solvent. The
structures of complexes 11a and 24, and of the hexafluorophosphate analogue (26) of complex
25, have been confirmed by X-ray crystallographic analyses. Carbene complex 1a , along with
other products, is also obtained upon reaction of 5 and Ph3P (1:1) with dimethylamine.
Formation of 1a in this case can proceed via two pathways, one involving cyclic ylide species
2a as intermediate and the other the N-protonated (dimethylamino)methyl complex cis-
[(Ph3P)Pt(CH2NHMe2)Cl2] (20). The mechanistic pathways involved in formation of carbene
complexes 1a -e and 25, ylide complexes 2a -e and 11a -e, and (dimethylamino)methyl
complex 20 are discussed. It is suggested that formation of the ylide complexes and 20
proceeds via initial attack of amine at platinum and that carbene formation proceeds via
platinum(IV) carbene hydride intermediates.
In tr od u ction
composition of the cyclic ammonium ylide complex 2a
(Scheme 1). The latter was obtained7 by reaction of
(Ph3P)3Pt with the Mannich salt [Me2NCH2]Cl. Decom-
position of 2a was suggested7 to proceed, as outlined in
Scheme 1, via displacement of the coordinated dimeth-
ylamino group by the chloride counterion followed by
fragmentation of the resulting intermediate (3a ) to
release the Mannich cation which then abstracts hy-
dride from the accompanying fragment (4a ) to give
Halomethyl complexes of transition metals have at-
tracted increasing attention in recent years as precur-
sors to a wide range of products formed by replacement
of the halogen by nucleophilic species.1 We have re-
ported preparative routes2 to a series of both mono- and
bis(chloromethyl)platinum(II) derivatives, and we, and
others, have described replacement reactions of certain
of these derivatives involving nitrogen,3 phosphorus,4
oxygen,3,5 and sulfur6 nucleophiles. The present study
was suggested by the reported7 formation of the [(di-
methylamino)carbene]platinum(II) complex 1a via de-
(4) (a) Kermode, N. J .; Lappert, M. F.; Skelton, B. W.; White, A. H.;
Holton, J . J . Organomet. Chem. 1982, 228, C71-C75. (b) Engelter, C.;
Ross, J . R.; Nassimbeni, L. R.; Niven, M. L.; Reid, G.; Spiers, J . C. J .
Organomet. Chem. 1986, 315, 255-268. (c) Hoover, J . F.; Stryker, J .
M. Organometallics 1988, 7, 2082-2084. (d) McCrindle, R.; Ferguson,
G.; Arsenault, G. J .; Hampden-Smith, M. J .; McAlees, A. J .; Ruhl, B.
L. J . Organomet. Chem. 1990, 390, 121-126.
(5) Hoover, J . F.; Stryker, J . M. J . Am. Chem. Soc. 1989, 111, 6466-
6468.
(6) McCrindle, R.; Arsenault, G. J .; Farwaha, R. J . Organomet.
Chem. 1985, 296, C51-C53.
(7) Barefield, E. K.; Carrier, A. M.; Sepelak, D. J .; Van Derveer, D.
G. Organometallics 1982, 1, 103-110.
* To whom correspondence should be addressed. E-mail: mccrindle@
chembio.uoguelph.ca.
(1) See e.g.: Friedrich, H. B.; Moss, J . R. J . Organomet. Chem. 1993,
453, 85-95 and references therein.
(2) McCrindle, R.; Arsenault, G. J .; Farwaha, R.; Hampden-Smith,
M. J .; Rice, R. E.; McAlees, A. J . J . Chem. Soc., Dalton Trans. 1988,
1773-1780.
(3) McCrindle, R.; Ferguson, G.; McAlees, A. J . J . Chem. Soc., Chem,
Commun. 1990, 1524-1526.
10.1021/om990049h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/29/1999

Formation of (Dimethylamino)carbene Complexes
Organometallics, Vol. 18, No. 13, 1999 2429
Sch em e 1
Sch em e 2
trimethylamine and the carbene complex, 1a . It oc-
curred to us that it might be possible to generate
complexes of type 2a, and consequently (dimethylamino)-
carbene complexes, by reaction of (chloromethyl)plati-
num(II) complexes with N,N,N′,N′-tetramethylmethane-
diamine. Formation of 2a and analogues by reactions
of this type might conceivably proceed via initial attack
of the diamine at platinum or at carbon. There are a
number of reports of the formation of cyclic ylide
complexes from (halomethyl)metal or related derivatives
and potentially bidentate ligands, in particular those
with phosphorus, arsenic, or sulfur donor atoms.6,8
Consideration of potential (chloromethyl)platinum(II)
precursor complexes for reaction with Me2NCH2NMe2
led us to investigate the approach outlined in Scheme
2. Sequence 1 envisages starting from the known2
complex [(COD)Pt(CH2Cl)Cl] (5; COD ) 1,5-cycloocta-
diene). It has been observed6 that complex 5 does not
react with the diamine Me2NCH2CMe2CH2NMe2 (CDCl3,
room temperature, 12 h), although the bis(sulfide)
MeSCH2CEt2CH2SMe does react slowly (days at room
temperature) to give the cyclic sulfonium ylide complex
6. It was therefore anticipated that Me2NCH2NMe2
would not react with 5 alone, at least under relatively
mild conditions. However, it seemed possible that ad-
dition to the reaction mixture of 1 equiv (vs 5) of a
monodentate ligand (L in Scheme 2) capable of displac-
ing COD from 5 would produce a mixture containing at
least a trace of reactive species 8, which might be, for
example, the dimer [LPt(CH2Cl)Cl]2,9 [LPt(CH2Cl)Cl-
(η2-COD)], or [LPt(CH2Cl)Cl(solvent)], in equilibrium.
Reactive intermediate 8 could then give the desired
cyclic ammonium ylide complex 2 via attack of Me2-
NCH2NMe2 at platinum to give species 9 followed by
internal displacement of chloride from the chloromethyl
group. Alternatively, reaction might proceed by initial
replacement of the chloride of the chloromethyl group
in [L2Pt(CH2Cl)Cl] (7; Scheme 2) by Me2NCH2NMe2 to
give intermediate 1010 followed by intramolecular dis-
placement of ligand L. Given the bulky nature of Me2-
NCH2NMe2, it seemed unlikely that reaction at the
chloromethyl group of 7 could proceed via an SN2-like
process. However, attack at carbon would be feasible if
preceded by either dissociation of the alkyl chloride (to
give a reactive four-coordinate cationic carbene species)
or migration of chloride from carbon to platinum (to give
a five-coordinate, neutral carbene intermediate).11
Resu lts a n d Discu ssion
Rea ction s w ith L ) P P h 3. (a ) In itia l Stu d ies. The
feasibility of proposed sequence 1 (Scheme 2) was first
explored by monitoring the reaction of equimolar quan-
tities of [(COD)Pt(CH2Cl)Cl] (5), PPh3, and Me2NCH2-
1
NMe2 in CDCl3 at ambient temperature in air. H and
31P NMR spectra12 (Tables 1 and 2) run immediately
after mixing showed that all of the phosphine had
reacted with the COD complex to give trans-[(Ph3P)2-
Pt(CH2Cl)Cl]2 (7a ), so that the solution now contained
5, 7a , the diamine, and free COD in a 0.5:0.5:1:0.5 mol
ratio, respectively (see Chart 1 for the structures of all
compounds discussed in this paper). Over the course of
several hours the growth of new NMR signals attribut-
able to the cyclic ammonium ylide complex 2a could be
(8) (a) Weber, L.; Wewers, D. Chem. Ber. 1984, 117, 732-742, 1103-
1112. (b) Weber, L.; Wewers, D. Organometallics 1985, 4, 841-846.
(c) Paul, W.; Werner, H. Chem. Ber. 1985, 118, 3032-3040. (d) Werner,
H.; Hofmann, L.; Paul, W.; Schubert, U. Organometallics 1988, 7,
1106-1111. (e) Alcock, N. W.; Pringle, P. G.; Bergamini, P.; Sostero,
S.; Traverso, O. J . Chem. Soc., Dalton Trans. 1990, 1553-1556. (f)
Annan, T. A.; Tuck, D. G.; Khan, M. A.; Peppe, C. Organometallics
1991, 10, 2159-2166. (g) McCrindle, R.; Ferguson, G.; McAlees, A. J .;
Arsenault, G. J .; Gupta, A.; J ennings, M. C. Organometallics 1995,
14, 2741-2748.
(9) Dimeric complexes of the type [LPt(Ph)Cl]2 have been obtained
by treating [(COD)Pt(Ph)Cl] with bulky phosphine ligands, while less
sterically demanding monodentate ligands give the bis(phosphine)
derivatives trans-[L2Pt(Ph)Cl] with no detectable (by NMR) dimeric
product, even with a deficiency of ligand, L (Anderson, G. K.; Clark,
H. C.; Davies, J . A. Inorg. Chem. 1981, 20, 3607-3611).
(10) The species 10 (Scheme 2, L ) PPh3) is a likely intermediate
in the formation of cyclic ammonium ylide complex 2a 7 in the
preparation outlined in Scheme 1.
(11) Although the mechanism is presently unknown, our finding3
that trans-[(R3P)2Pt(CH2Cl)Cl] (R ) Et, cyclohexyl) can be converted
cleanly to trans-[(R3P)2Pt(CH2OMe)Cl] may suggest that initial attack
at carbon is feasible.
(12) 1H and 31P NMR data are collected in Tables
respectively.
1 and 2,

2430 Organometallics, Vol. 18, No. 13, 1999
Ferguson et al.
Ta ble 1. 1H NMR Da ta
Ta ble 2. 31P NMR Da ta
1J Pt-P
Hz
,
1J Pt-P
Hz
,
1J Pt-P
,
Hz
(a) Pt-CH Protons
compd
δP
compd
δP
compd
δP
compd
δH
3J P-H, Hz
2J Pt-H, Hz
1a
1b
1c
1d
2a
2b
2c
8.35 4044
3.88 4044
5.92 4069
10.17 3747
10.63 4047
5.79 4065
8.45 4099
7a
7b
7c
7d
11a
11b
11c
11d
27.40 3155
23.22 3103
24.53 3177
14
16
17
18
19a
21
24
13.57 4395
17.71 2613
7.66 3344
15.53 4141
3.90 3524
14.25 4368
16.12 4125
1a
1b
1c
1d
1e
2a
2b
2c
2e
7a
7b
7c
9.82 (d, 1H)
9.83 (d, 1H)
9.84 (d, 1H)
10.58 (d, 1H)
10.09 (s, 1H)
3.21 (br s, 2H)
3.21 (d, 2H)
3.26 (d, 2H)
3.37 (s, 2H)
3.03 (t, 2H)
2.97 (t, 2H)
2.89 (t, 2H)
3.69 (t, 2H)
3.17 (s, 2H)
3.63 (d, 2H)
3.62 (d, 2H)
3.63 (d, 2H)
3.91 (d, 2H)
3.62 (s, 2H)
3.47 (d, 2H)
10.41 (br, 1H)
10.09 (br, 1H)
3.47 (d, 2H)
4.02 (d, 2H)
1.34 (m, 2H)
11.09 (s, 1H)
∼3 (br m, 2H)
10.37 (s, 1H)
3.29 (d, 2H)b
4.0
4.0
3.6
4.1
22
20
20
42
a
53
a
a
a
52
a
56
56
59.6
75
a
16.0
2793
13.56 4407
9.18 4410
11.25 4410
4.33 4115
a
2.5
2.5
a
Cf. ref 16.
8
9
8
8.8
species present in solution was the carbene complex 1a ,
but this was accompanied by a significant quantity of
the more polar product 11a , which was separated from
1a and accompanying byproducts by preparative TLC.
Its formulation as the trimethylammonium ylide com-
plex 11a has been confirmed by an X-ray crystal
structure analysis (see below). Trimethylamine, liber-
ated in the course of the conversion of 2a into 1a , is
presumably the source of the Me3N moiety in 11a . Since
this complex was not obtained from the decomposition
of pure 2a ,7 it must form via reaction of trimethylamine
with COD complex 5, bis(phosphine) complex 7a , or
some species (e.g. 8) derived therefrom. The relative
amounts of 11a formed could be reduced by using excess
diamine in the reaction, although a concomitant in-
crease in the amounts of other byproducts was observed
(see later). Interestingly, the overall rate of reaction did
not change appreciably with increasing amine concen-
tration.13
7d
7e
11a
11b
11c
11d
11e
14
16
17
18
21
24
25
4.6
4.4
4.4
3.7
a
72
81
77
26
28
52
50
77
48
a
4.4
a
a
4.8
2.5
a
26
48
57
(b) N-Methyl Protons
J Pt-H
,
J Pt-H
Hz
,
compd
δH
Hz
compd
δH
1a
1b
1c
1d
1e
2a
2b
2c
2e
2.85 (s, 3H)
3.52 (s, 3H)
2.89 (s, 3H)
3.52 (s, 3H)
2.96 (s, 3H)
3.55 (s, 3H)
3.48 (s, 3H)
3.81 (s, 3H)
2.85 (s, 3H)
3.56 (s, 3H)
3.27 (d, 6H)c
3.40 (s, 6H)
3.23 (s, 6H)
3.41 (s, 6H)
3.31 (br s, 6H)
3.47 (s, 6H)
3.29 (s, 6H)
3.43 (s, 6H)
11a
11b
11c
11d
11e
14
2.76 (s, 9H)
2.79 (s, 9H)
2.83 (s, 9H)
3.22 (s, 9H)
2.57 (s, 9H)
2.56 (s, 6H)
2.61 (s, 3H)
3.04 (s, 3H)
2.75 (dd, 6H)d
3.00 (s, 3H)
3.50 (s, 3H)
2.87 (dd, 6H)e
2.74 (dd, 6H)f
2.88 (d, 6H)g
2.97 (br s, 6H)
2.93 (s, nH)h
3.22 (s, nH)h
2.87 (s, 3H)
2.96 (d,i 6H)
3.21 (s, 3H)
While essentially complete conversion of starting
materials to products 1a and 11a required more than 1
week at ambient temperature, the reaction time could
be reduced to a few hours by heating the CDCl3 solution
to 60-65 °C, although a somewhat higher proportion
of (trimethylammonio)methyl complex 11a was obtained
under these conditions. On a preparative scale, with
heating, yields of 1a and 11a of 60-65% and 15-20%,
respectively, could be obtained when the solvent was
relatively dry. When CHCl3 stabilized with 0.75% of
ethanol was used as solvent, products 1a and 11a were
accompanied by the dimethyl(ethoxymethyl)ammonium
ylide complex 14, which could be prepared, in good yield,
by allowing a solution containing equimolar quantities
of COD complex 5, PPh3, and an authentic sample of
EtOCH2NMe2 to stand at ambient temperature.14
12
9.5
9.5
11
16
20
32
17
10.1
22
9.6
18
19
21
24
25
30
24
24
a
a
a
a
a
26
11
(c) NCH2N and NCH2O Protons
(b) Min or P r od u cts, a n d Use of NHMe2 in stea d
of Me2NCH2NMe2. Small quantities of various byprod-
ucts, the relative amounts presumably depending on the
purity of the solvent, were usually detected in the
reaction solutions. Thus, the hydride complex trans-
J Pt-H
,
J Pt-H,
Hz
compd
δH
Hz
compd
δH
2a
2b
2c
4.97 (br s, 2H)
4.97 (br s, 2H)
5.16 (br s, 2H)
27
a
a
2e
14
21
4.99 (s, 2H)
4.33 (s, 2H)
3.67 (d, 2H)j
33
39
a
b
Obscured or not resolved. s after D2O exchange (3J NH-H
)
(13) Surprisingly, excess diamine did not appear to hinder conver-
sion of 2a into 1a , although one would expect liberated Mannich cation
to be trapped with the resulting formation of a complex such as
[(Ph3P)Pt(η2-CH2NMe2)Cl] (12). The last was the product initially
expected from reaction7 of (Ph3P)3Pt with [Me2NCH2]Cl, since the
nickel analogue had been obtained by this route. Indeed, preparative
TLC of solutions containing 2a gave fractions containing a component
the NMR spectra of which would be consistent with structure 12 or
the related dimer 13 (see Experimental Section). This compound, upon
standing in CDCl3, was slowly converted into carbene complex 1a .
(14) Solutions of 14 show no sign of decomposition, even upon
heating to 60-65 °C, to give carbene complex 1a and EtOMe. Such a
reaction would be analogous to the formation of 1a and trimethylamine
from cyclic intermediate 2a via 3a (Scheme 1).
c 4
d
4
3
5.6 Hz).
J
J
J
) 3.5 Hz. J P-H ) 4.0 Hz; J NH-H ) 5.6 Hz.
P-H
f 4
) 3.5 Hz; 3J NH-H ) 6.2 Hz.
J
) 3 Hz; 3J NH-H ) 4 Hz.
P-H
e 4
P-H
) 2.8 Hz. Singlets superimposed on broad resonances.i s
g 4
h
P-H
after D2O exchange (3J NH-H ) 5.2 Hz). J P-H ) 1.2 Hz.
j
observed. After 1 day, (dimethylamino)carbene complex
1a could be detected. Essentially complete disappear-
ance of signals due to the starting COD complex, the
initially generated bis(phosphine) complex, and the ylide
complex required about 10 days at ambient tempera-
ture. At this stage, the major platinum-containing

Formation of (Dimethylamino)carbene Complexes
Organometallics, Vol. 18, No. 13, 1999 2431
Ch a r t 1a
a
Legend: a , L ) Ph3P; b, L ) (4-MeOC6H4)3P; c, L ) (4-FC6H4)3P; d , L ) Et3P; e L ) Ph3As.
[(Ph3P)2Pt(CH2Cl)H] (15), which can be formed15 from
chloromethyl complex 7a in the presence of water, was
often detected. In addition, cis- and, occasionally, trans-
[(Ph3P)2PtCl2], presumably resulting15 from further
reaction of 15, and (COD)PtCl2 were found. Occasion-
solvent leads to partial decomposition of 17 and regen-
eration of 1a , while preparative TLC gives only 1a .
In some cases, the first product detected, after the
initial rapid formation of bis(phosphine) complex 7a ,
showed NMR signals consistent with its formulation as
the chloromethyl dimethylamine complex 18. When
such a solution was allowed to stand until formation of
the main products, 1a and 11a , was complete, the NMR
signals due to 18 had disappeared. The resulting solu-
tion then showed, inter alia, weak signals assignable
to trans-[(Ph3P)(HNMe2)PtCl2]16 (19), which was iso-
lated by preparative TLC. When dimethylamine, most
conveniently added as the CO2 adduct, was reacted with
equimolar quantities of 5 and PPh3 in CDCl3, formation
of 18 proceeded largely to completion over a few hours
at ambient temperature. When the resulting solution
was allowed to stand, slow disappearance of 18 was
observed over a period of 10 days. During that time, new
signals ascribable to several products developed. These
included, not unexpectedly, hydride complex 15 and
1
ally, H NMR spectra of the solutions from reaction of
COD complex 5 with PPh3 and Me2NCH2NMe2 showed
one or two weak low-field signals (δ 10.41, 10.13)
characteristic of carbene complexes, in addition to that
of the major product 1a . Formation of these byproducts
was more pronounced in reactions where excess diamine
was employed. The signal at δ 10.41 can be ascribed to
the bis(phosphine) complex trans-[(Ph3P)2Pt(CHNMe2)-
Cl]Cl (16), which is also obtained when carbene complex
1a is treated with 1 equiv of PPh3, while the signal at
δ 10.13 corresponds to the dimethylamine analogue
trans(N,P)-[(Ph3P)(HNMe2)Pt(CHNMe2)Cl]Cl (17). Com-
plex 17 can be generated in solution by addition of
dimethylamine to 1a in CDCl3. Evaporation of the
(15) McCrindle, R.; Arsenault, G. J .; Gupta, A.; Hampden-Smith,
M. J .; Rice, R. E.; McAlees, A. J . J . Chem. Soc., Dalton Trans. 1991,
949-954.
(16) Al-Najjar, I. M.; Green, M.; Kerrison, S. J . S.; Sadler, P. J . J .
Chem. Res., Synop. 1979, 206-207.

2432 Organometallics, Vol. 18, No. 13, 1999
Ferguson et al.
amine phosphine complex 19, and also the known cyclic
ylide species 2a , carbene complex 1a , and (trimethyl-
ammonio)methyl complex 11a . However, we were un-
able to find any signals that could be ascribed to a
complex containing a PtCH2NMe2 moiety, e.g. species
12 or 13.13 At the end of the reaction, 1a , 11a , 15, and
19 were recovered by preparative TLC. The formation
of 2a in this reaction probably involves the participa-
tion of formaldehyde, formed by reaction15 of chlorom-
ethyl complex 7a (or 18)17 with traces of water in the
solvent.
(dimethylammonio)methyl complex 20. Upon standing,
gradual conversion into 1a was observed as before.
These experiments clearly demonstrate that, in the
reactions with dimethylamine, there are two pathways
leading to carbene complex 1a , one via cyclic intermedi-
ate 2a and a second via 20. Possible mechanisms are
discussed later.
(c) P r elim in a r y Mech a n ist ic Con sid er a t ion s.
Further studies were carried out with a view to obtain-
ing some insight into the mechanism of formation of
cyclic ammonium ylide complex 2a in our original
reaction. Thus, no reaction was detected when CDCl3
solutions of either COD complex 5 plus diamine or bis-
(phosphine) complex 7a plus diamine were allowed to
stand for several days at ambient temperature. How-
ever, addition of 5, or of [(COD)PtCl2], to the latter
solution resulted in reaction to give intermediate 2a and
then products 1a and 11a , as before. These results
appear to rule out any mechanism of formation of 2a
involving initial nucleophilic displacement on the chlo-
romethyl groups of complexes 5 or 7a , since such a C-N
bond-forming step would be expected to be irreversible
under the reaction conditions employed. Indeed, reaction
via initial attack at platinum would be consistent with
the observed formation of complex 18 in the reaction
with dimethylamine. However, direct displacement by
the bulky diamine of either COD, from 5, or PPh3, from
7a , is expected to be very unfavorable, as borne out by
the lack of any observable reaction in the experiments
described above.19 The observation that 5, or [(COD)-
PtCl2], promotes the reaction suggests that these com-
plexes act as acceptors of a phosphine ligand from 7a ,
thereby facilitating what would otherwise be an ener-
getically unfavorable step. This could involve formation
of a reactive species (8, L ) PPh3; Scheme 2) having
the type of structure indicated in the introductory
section, via reversible dissociation20 of a phosphine from
7a , followed by attack on the reactive species by the
diamine to give 9a . This is consistent with the observa-
tion that the overall reaction rate does not change with
increasing concentration of the diamine. In the absence
of a scavenger for PPh3, attack of the diamine on 8
apparently cannot compete with return of the phos-
phine. Subsequent conversion of 9a to cyclic ylide
complex 2a , e.g. by attack of the free end of the
coordinated diamine on the chloromethyl group, must
be relatively fast.
Attempts to isolate 18 were unsuccessful due to its
instability (see Experimental Section). However, the
results of these investigations revealed that formation
of 1a from 18 proceeds via at least one further route in
addition to that via 2a . When 18 was generated in
CDCl3 and this solution was added to a large volume of
hexane, the major product in the resulting gummy
precipitate was 20, which contains the novel N-proton-
ated (dimethylamino)methyl ligand. The latter moiety
is characterized by proton signals at δ 2.63 (6H, d, J )
5.6 Hz) and 2.70 (2H, m), both of which are coupled
(COSY) to a broad peak at δ 8.15 (1H, NH). When
solutions of 20 in CDCl3 were left at ambient temper-
ature, slow, and apparently clean, conversion to carbene
complex 1a was observed. The material obtained in the
attempted precipitation of 18 (above) accounted for less
than half of that expected. When the supernatant was
evaporated and the residue redissolved in CDCl3, 1H and
31P NMR spectra indicated that the solution contained
largely 18 along with small amounts of bis(phosphine)
complex 7a and hydride 15. When this solution was
allowed to stand, slow decomposition of 18 was again
observed, but a new major product was now generated.
This proved to be stable to preparative TLC, and NMR
(1H, 13C, and 31P) data and elemental analysis are
consistent with its formulation as 21, which contains a
chelating ((dimethylamino)methoxy)methyl ligand. This
product could arise via condensation of formaldehyde
with dimethylamine complex18 18 to give the dimethyl-
(hydroxymethyl)amine complex 22 followed by intramo-
lecular displacement on the chloromethyl group.
Since the above results indicate that the fate of
dimethylamine chloromethyl complex 18 depends criti-
cally upon the reaction conditions, a further series of
experiments was performed. (i) When 18 was generated
in CDCl3 using 1 equiv of dimethylamine (some 5 and
7a present), followed by the addition of paraformalde-
hyde and standing at ambient temperature, cyclic
complex 21 was formed as a major product. (ii) When
18 was generated as in (i), but using 2 equiv of
dimethylamine (little or no 5 or 7a present), addition
of paraformaldehyde resulted in initial significant for-
mation of cyclic intermediate 2a , with the eventual
major product being carbene complex 1a . (iii) When 18
was generated using excess dimethylamine, the solvent
evaporated, and the resulting gum pumped under
vacuum, then the major species detected by NMR was
Formation of (trimethylammonio)methyl product 11a
could then involve reaction of trimethylamine with 8
(19) It has been reported that addition of PPh3 to (COD)PtCl2 under
an atmosphere of CO, or to (COD)PtMe2 in the presence of amines,
leads to cis-[(Ph3P)Pt(CO)Cl2]9 or cis-[(Ph3P)(amine)PtMe2] (see: Thorn,
D. L.; Calabrese, J . C. J . Organomet. Chem. 1988, 342, 269-280)
presumably via trapping of η1-COD intermediates, formed upon initial
reaction of the phosphine, by CO or amine, respectively. A similar
pathway in the present case would be expected to lead to cyclic
intermediate 2a via species 9a . However, slow addition of PPh3 (5 min)
to a solution of 5 and Me2NCH2NMe2 in CDCl3 did not result in an
observable increase in the rate of formation of 2a , the only detectable
initial products being bis(phosphine) complex 7a and free COD.
(20) Initial reversible dissociation of phosphine is believed to be
involved in various reactions of complexes of the type trans-[L2Pt(R)X]
(L ) phosphine). See e.g.: (a) Arnold, D. P.; Bennett, M. A. Inorg.
Chem. 1984, 23, 2110-2116. (b) Flood, T. C.; Statler, J . A. Organo-
metallics 1984, 3, 1795-1803. (c) Brainard, R. L.; Miller, T. M.;
Whitesides, G. M. Organometallics 1986, 5, 1481-1490. (d) Sen, A.;
Chen, J .-T.; Vetter, W. M.; Whittle, R. R. J . Am. Chem. Soc. 1987,
109, 148-156. (e) Stang, P. J .; Kowalski, M. H. J . Am. Chem. Soc.
1989, 111, 3356-3362. (f) Edelbach, B. L.; Vicic, D. A.; Lachicotte, R.
J .; J ones, W. D. Organometallics 1998, 17, 4784-4794.
(17) The amount of hydride 15 formed in these reactions, and its
relatively rapid appearance, may indicate that 18 is the major source.
Formation of 15 from bis(phosphine) complex 7a alone was very slow.15
(18) Condensations involving formaldehyde and coordinated amines
are well-known. See e.g.: Bottomley, G. A.; Clark, I. J .; Creaser, I. I.;
Engelhardt, L. M.; Geue, R. J .; Hagen, K. S.; Harrowfield, J . M.;
Lawrance, G. A.; Lay, P. A.; Sargeson, A. M.; See, A. J .; Skelton, B.
W.; White, A. H.; Wilner, F. R. Aust. J . Chem. 1994, 47, 143-179.

Formation of (Dimethylamino)carbene Complexes
Organometallics, Vol. 18, No. 13, 1999 2433
(L ) PPh3) to give intermediate 23. Conversion of the
latter to 11a effectively requires migration of the Me3N
ligand from platinum to carbon, with concomitant
displacement of chloride, which migrates to platinum.
This type of mechanism21 has been proposed for the
formation of the rhodium(III) ylide complex [(η5-
C5H5)Rh(PMe3)(CH2PMe3)I]I from [(η5-C5H5)Rh(PMe3)2-
(CH2I)]I and related reactions. Formation of (dimethyl-
(ethoxymethyl)ammonio)methyl complex 14 from Me2-
NCH2OEt presumably proceeds similarly, and indeed,
an alternative mode of formation of cyclic intermediate
2a could involve the sequence 9a f 3a f 2a . Formation
of 20 from chloromethyl dimethylamino complex 18 may
proceed similarly. Migration of dimethylamine is sig-
nificantly slower than that of trimethylamine,22 prob-
ably due to a combination of the lower steric bulk of
the former amine and the possibility of its forming a
hydrogen bond to the neighboring Cl in 18.23
carbene derivatives via sequence 1 (Scheme 2) provided
examples where either the formation of cyclic interme-
diate 2, or its breakdown to carbene complex 1, is
significantly slower than found for the arylphosphine
derivatives.
The former situation was encountered for L ) PEt3.
In this case, the ligand was most conveniently intro-
duced as the previously described chloromethyl complex
7d .15 Thus, a solution containing COD complex 5, 7d ,
and Me2NCH2NMe2 in CDCl3 showed no sign of reaction
on standing at ambient temperature for up to 3 days.
However, upon heating at 55 °C the reaction proceeded
to produce a mixture containing 1d and 11d . The slower
reaction in this case might be rationalized if it proceeds
through cyclic intermediate 2d , formed via initial attack
of the diamine at platinum to give 9d , since this would
24
require breaking of a relatively strong bond to PEt3
in 7d .
(d ) Rea ction in Aceton itr ile. In the earlier work7
carbene complex 1a was obtained by heating a solution
of cyclic ammonium ylide complex 2a in acetonitrile. We
have therefore briefly investigated the use of this solvent
The relatively stable cyclic ammonium ylide complex
2e was formed when equimolar quantities of 5, Ph3As,
and Me2NCH2NMe2 were left at ambient temperature
in CDCl3. As with the arylphosphine ligands, rapid
initial reaction gave the bis(arsine) complex 7e. Subse-
quent formation of cyclic complex 2e proceeded more
rapidly than that of the aryl phosphine analogues 2a -
c, being complete within 1 day at ambient temperature.
Complex 2e showed little sign of decomposition over a
few days at this temperature, but decomposition could
be induced by heating at 55 °C. When decomposition of
2e was complete, the 1H NMR spectrum of the resulting
solution showed two low-field resonances (δ 11.09 and
10.09) characteristic of protons attached to carbene C
atoms. Preparative TLC of this solution gave two major
products, the less polar of which proved to be the desired
carbene complex, 1e. The 1H NMR spectrum of the more
polar product (25) showed, in addition to the carbene
proton resonance at δ 11.09 and signals due to coordi-
nated Ph3As, a broad D2O-exchangeable signal (δ 10.0,
NH) and two sharp peaks (δ 2.93 and 3.22, NMe’s)
superimposed on broad, overlapping resonances.25 Since
the polarity of this material, and the broadened signals
in its proton spectrum, suggested an ionic species,
presumably a chloride salt, it was subjected to ion
exchange with excess KPF6. The resulting product gave
1
in our reaction. Monitoring by H and 31P NMR spec-
troscopy indicated that the reaction in CD3CN was
complete within 2 h at temperatures in the range 60-
70 °C but that major products 1a and 11a were
accompanied by a third significant product (24). These
three products were isolated from a preparative-scale
reaction in CH3CN, and the structure of 24 was estab-
lished by X-ray crystallographic analysis (see below).
Although we have not undertaken studies of the mech-
anism of formation of 24, we have observed that the
product obtained from CD3CN solution contains the
deuterated moiety -CH2CD2C(O)NMe2, suggesting that
its formation involves coupling of a -CH2Cl (or derived)
fragment with a molecule of solvent.
Rea ction s w ith L ) (4-MeOC6H4)3P a n d (4-F C6-
H4)3P . The aryl phosphines (4-MeOC6H4)3P and (4-
FC6H4)3P were found to behave similarly to PPh3, giving
initially the trans-bis(phosphine) complexes 7b,c fol-
lowed by the cyclic ammonium ylide intermediates 2b,c
and then the corresponding carbene complexes 1b,c
along with the (trimethylammonio)methyl derivatives
11b,c. While the reactions of all three arylphosphines
proceeded at very similar overall rates, it was observed
(31P NMR) that the ratio of carbene complex to tri-
methylammonio complex formed in these reactions
decreased in the order (4-FC6H4)3P > PPh3 > (4-
MeOC6H4)3P. The differences are small, but they do
suggest that the rate of formation of intermediate 2
increases relative to its rate of decomposition in the
same order, viz. (4-FC6H4)3P > PPh3 > (4-MeOC6H4)3P.
Presumably, formation of 2b,c proceeds, as discussed
above for 2a , via short-lived intermediates 9b,c.
1
a sharp H NMR spectrum, consistent with its formula-
tion as 26. This structure was confirmed by an X-ray
crystallographic study (see below).
Further investigation of the reaction with Ph3As led
to the following observations. (i) When a solution of 5,
Ph3As, and Me2NCH2NMe2 (1:1:2) in CDCl3 was heated
from the outset, the resulting product mixture included
the (trimethylammonio)methyl complex 11e. (ii) The bis-
(arsine) complex 7e reacts with Me2NCH2NMe2 at
ambient temperature in the absence of COD complex 5
to give cyclic species 2e plus free Ph3As. The rate of
formation of 2e was somewhat slower than what was
found for the reaction in the presence of 5, requiring
more than 1 day to reach completion. The reactivity of
7e contrasts with that of the PPh3 analogue 7a . If initial
Rea ction s w ith L ) Et3P a n d P h 3As. Further
investigations of the preparation of (dimethylamino)-
(21) Werner, H.; Hofmann, L.; Feser, R.; Paul, W. J . Organomet.
Chem. 1985, 281, 317-347.
(22) The presumed intermediate 23 has not been detected.
(23) For recent examples of hydrogen bonds involving four-mem-
bered rings, see: Petrucci, M. G. L.; Lebuis, A.-M.; Kakkar, A. K.
Organometallics 1998, 17, 4966-4975. For a recent survey of crystal
structures involving hydrogen bonds between metal-bound chlorine and
hydrogen donors, including H-N groups, see: Aullon, G.; Bellamy, D.;
Brammer, L.; Bruton, E. A.; Orpen, A. G. Chem. Commun. 1998, 653-
654.
(24) Atwood, J . D. Inorganic and Organometallic Reaction Mecha-
nisms; Brooks/Cole: Monterey, CA, 1985; pp 120-121.
(25) Sometimes an additional weak low-field signal was observed
at δ 10.0 (superimposed on the D2O-exchangeable signal). This was
probably due to the presence of some trans(As,N)-[(Ph3As)(HNMe2)-
Pt(CHNMe2)Cl]Cl (cf. phosphine analogue 17).

2434 Organometallics, Vol. 18, No. 13, 1999
Ta ble 3. Su m m a r y of P r in cip a l Dim en sion s (Å, d eg) for 11a , 24 a n d 26
Ferguson et al.
Compound 11a
C1-Pt1-Cl1
C1-Pt1-Cl2
C1-Pt1-P1
Cl1-Pt1-Cl2
Pt1-C1
Pt1-Cl1
Pt1-Cl2
Pt1-P1
2.041(7)
2.3495(18)
2.387(2)
C1-N1
C2-N1
C3-N1
C4-N1
1.569(8)
1.475(9)
1.509(10)
1.419(10)
89.3(2)
178.0(2)
95.7(2)
Cl1-Pt1-P1
Cl2-Pt1-P1
172.72(6)
86.20(7)
2.2169(18)
88.86(8)
C3-N1-C1-Pt1
-154.8(6)
Compound 24
C3-Pt1-Cl1
C3-Pt1-O1
C3-Pt1-P1
Cl1-Pt1-O1
Cl1-Pt1-P1
O1-Pt1-P1
Pt1-C3
Pt1-Cl1
Pt1-O1
Pt1-P1
2.057(10)
2.387(2)
2.052(8)
2.209(2)
C1-C2
C1-N1
C1-O1
C2-C3
C4-N1
C5-N1
1.513(14)
1.316(12)
1.321(11)
1.530(14)
1.435(14)
1.460(11)
169.5(3)
81.6(4)
91.5(3)
87.9(2)
98.98(9)
173.1(2)
C1-C2-C3
112.1(8)
117.8(6)
115.1(8)
110.2(7)
-2.3(17)
176.5(10)
C1-O1-Pt1
C2-C1-O1
C2-C3-Pt1
C4-N1-C1-O1
C5-N1-C1-O1
Compound 26
As1-Pt1-Cl
As1-Pt1-C5
As1-Pt1-Cl1
C1-Pt1-C5
C1-Pt1-Cl1
C5-Pt1-Cl1
Pt1-As1
Pt1-C1
Pt1-C5
Pt1-Cl1
2.4313(12)
2.053(10)
1.929(16)
2.366(4)
C1-N2
C3-N2
C4-N2
C5-N6
C7-N6
C8-N6
1.489(17)
1.537(16)
1.448(18)
1.24(2)
1.43(2)
1.492(19)
178.9(4)
91.8(4)
92.38(9)
87.1(6)
88.7(4)
175.3(4)
N2-C1-Pt1
114.6(8)
132.1(12)
168.3(9)
N6-C5-Pt1
C3-N2-C1-Pt1
C4-N2-C1-Pt1
C7-N6-C5-Pt1
C8-N6-C5-Pt1
-67.7(13)
-1(2)
-177.3(11)
attack of the diamine takes place at Pt (to give 9e)
rather than at C, this would be consistent with the
expected greater lability of Pt-As versus Pt-P bonds.24
(iii) Reaction of 5, Ph3As, and diamine proceeds in C6D6
at a rate similar to that found in CDCl3, suggesting that
the slow step in the formation of 2e does not involve
ionization of the C-Cl bond (or indeed of the Pt-Cl
bond) in bis(arsine) intermediate 7e. This is consistent
with reaction via initial attack of diamine at Pt rather
than C. (iv) The relative stability of the arsine-contain-
ing cyclic intermediate 2e allowed us to investigate the
influence on its rate of formation of different initial
concentrations of Me2NCH2NMe2. Thus, no increase in
the rate of formation of 2e was observed when CDCl3
solutions prepared using the same initial quantities of
5 and Ph3As were treated with 2, 4, 8, or 16 equiv of
the diamine, suggesting that the rate-determining
step(s) in the formation of 2e does(do) not involve
participation of the diamine. When these solutions were
heated at 55 °C, decomposition of 2e to carbene com-
F igu r e 1. View of 11a with the numbering scheme. Phenyl
ring C atoms are labeled Ci1-Ci6 (i ) 1-3). Thermal
ellipsoids are drawn at the 30% probability level.
1
plexes 1e and 25 was observed as before. However, H
NMR spectra of the resulting solutions indicated that
the ratio of 1e to 25 decreases with increasing diamine
concentration. Indeed, at the highest diamine concen-
tration employed, the carbene proton signal for 1e was
no longer detectable.
longer than that in 1a (1.96(1) Å), reflecting, in part,
the difference between Pt-C(sp3) and Pt-C(sp2) σ-bonds.
Some contribution to the shortening of the Pt-C bond
in 1a relative to that in 11a may come from dπfpπ
back-bonding in the former. This contribution may be
reflected in the relative lengths of the Pt-Cl bonds trans
to C in the two complexes (2.347(3) and 2.387(2) Å,
respectively), with the shorter bond in 1a arising from
decreased repulsion between chlorine ligand lone pair
electrons and Pt d electrons26 due to PtfC π donation.
All other bond angles and lengths are in the expected
ranges.
(b) cis(C,P )-Ch lor o[2-(d im eth ylca r ba m oyl)eth yl-
C,O](tr ip h en ylp h osp h in e)p la tin u m (II) (24). A view
of the molecule is shown in Figure 2. The X-ray analysis
establishes the presence of the chelating -CH2CH2C-
(O)NMe2 ligand and the trans disposition of the phos-
phine ligand with respect to the coordinated carbonyl
oxygen. The coordination about platinum is essentially
square planar with some deviation of the in-plane angles
from the ideal 90° (O(1)-Pt(1)-C(3) ) 81.6(4)° and
P(1)-Pt(1)-Cl(1) ) 98.98(9)°). The conformation adopted
by the chelate ring is best described as an envelope with
X-r a y Cr ysta llogr a p h ic Stu d ies. (a ) cis-Dich lor o-
[(tr im eth ylam m on io)m eth yl](tr iph en ylph osph in e)-
p la tin u m (II) (11a ). A view of the molecule is shown
in Figure 1. Principal dimensions for this complex (and
for complexes 24 and 26 discussed below) are listed in
Table 3, and full details are given in the Supporting
Information. The chlorine ligands are cis in an ap-
proximately square-planar platinum coordination sphere.
A tetrahedral distortion is shown by the displacement
of the coordinating atoms from the least-squares plane
through Pt(1), Cl(1), Cl(2), P(1), and C(1). This distortion
and the Pt-P-C angle (95.7(2)°) reflect a steric interac-
tion between the bulky triphenylphosphine and (tri-
methylammonio)methyl ligands. It is interesting to
compare the platinum-ligand bond lengths for this
complex with those reported7 for the structurally related
carbene complex 1a . The Pt-P bond lengths are es-
sentially identical (2.2169(18) and 2.220(2) Å, respec-
tively), as are the Pt-Cl bond lengths for the Cl trans
to P (2.3495(18) and 2.345(3) Å, respectively). Not
surprisingly, the Pt-C distance in 11a (2.041(7) Å) is
(26) Caulton, K. G. New J . Chem. 1994, 18, 25-41.

Formation of (Dimethylamino)carbene Complexes
Organometallics, Vol. 18, No. 13, 1999 2435
Ta ble 4. Su m m a r y of Cr ysta l Da ta , Da ta Collection , Str u ctu r e Solu tion , a n d Refin em en t Deta ils
11a
24
26
(a) Crystal Data
formula
molar mass
color, habit
cryst size, mm
cryst syst
a, Å
C
22H26Cl2NPPt
C23H25ClNOPPt
592.95
colorless, plate
0.41 × 0.15 × 0.01
triclinic
C24H31AsClN2PPtPF6‚0.82CH2Cl2
601.40
colorless, needle
867.58
colorless, plate
0.42 × 0.31 × 0.20
triclinic
8.7724(16)
10.3240(17)
18.441(3)
76.309(15)
84.86(2)
86.967(15)
1615.3(5)
P1h
0.39 × 0.14 × 0.11
orthorhombic
9.8281(16)
27.674(4)
16.750(3)
90
7.9253(16)
8.9490(19)
16.763(8)
92.37(2)
97.42(3)
111.127(14)
1094.7(6)
P1h
b, Å
c, Å
R, deg
â, deg
90
90
γ, deg
V, Å3
4555.8(12)
Pbca
8
space group
Z
2
2
F(000)
2336
1.754
6.472
576
1.799
6.617
841
1.784
5.680
d
calcd, g cm-3
µ, mm-1
(b) Data Acquisitiona
temp, K
294(1)
294(1)
294(1)
unit cell rflns (θ range), deg
max. θ for rflns, deg
hkl range of rflns
decay in 3 std rflns
no. of rflns measd
no. of unique rflns
Rint
8.8-11.9
5.8-11.9
9.5-17.5
26.93
26.88
25.01
0-12; 0-35; 0-21
0.5
4965
4965
-10 to +9; 0-11; -21 to +21
8.6
4743
4743
-10 to +10; 0-12; -20 to +21
12.6
6138
5743
0.018
no. of rflns with I > 2σ(I)
2491
ψ scans
0.3514, 0.4970
3374
ψ scans
0.3609, 0.9167
4137
Gaussian
0.1724, 0.3707
abs cor type
min, max abs cor
(c) Structure Solution and Refinementb
refinement on
F2
F2
F2
soln method
Patterson heavy atom
riding
Patterson heavy atom
riding
Patterson heavy atom
riding
H-atom treatment
no. of variables in least squares
weights kc
247
255
434
(0.0361P)2
0.037, 0.073, 0.90
-0.961, 1.151
0.002
(0.0651P)2
0.044, 0.104, 1.00
-2.199, 2.636
0.002
(0.1002P)2 + 2.8184P
0.061, 0.164, 1.05
-0.766, 1.979
0.027
R, Rw, GOF
density range in final ∆-map, e Å-3
final shift/error ratio
a
b
Data collection on an Enraf-Nonius CAD4 diffractometer with graphite-monochromatized Mo KR radiation (λ ) 0.710 67 Å). All
calculations were done on a Dell Inspiron 3200 laptop computer with the NRCVAX system of programs (Gabe, E. J .; Le Page, Y.; Charland,
J .-P.; Lee, F. L.; White, P. S. J . Appl. Crystallogr. 1989, 22, 384-389) for refinement with observed data on F or with SHELXL-97 (G. M.
Sheldrick, 1997) for refinement with all data on F2. c w ) 1/(σ2Fo + k); P ) (Fo + 2Fc2)/3.
2
2
C(3) as the flap. The dihedral angle between the Pt(1)-
O(1)-C(1)-C(2) segment and the coordination plane is
only 7.64(0.58)°. The framework atoms of the carbamoyl
group show no significant deviation from planarity.
Bond lengths and all other bond angles are in the
expected ranges.
(c) tr a n s(As,CH2)-Ch lor o[(d im eth yla m in o)m eth -
ylene][(dimethylammonio)methyl](triphenylarsine)-
p la tin u m (II) Hexa flu or op h osp h a te (26). Analysis of
the structure of 26 was complicated by disorder in the
orientations of the phenyl groups of the arsine ligand,
for which two conformations were found, and by the
presence of solvent dichloromethane in the crystal
lattice. In addition, significant degradation of the crystal
took place in the course of data collection (see Table 4).
The structure consists of discrete four-coordinate cations
F igu r e 2. View of 24 with the numbering scheme. Phenyl
ring C atoms are labeled Ci1-Ci6 (i ) 1-3). Thermal
ellipsoids are drawn at the 30% probability level.
and hexafluorophosphate anions. A view of the cation,
which depicts only the major conformation found for the
arsine ligand, is shown in Figure 3. The coordination
sphere of the cation is close to square planar, and the
analysis confirms the presence of a protonated (di-
methylamino)methyl ligand trans to the arsine. The
conformation adopted by the former ligand allows the
formation of a hydrogen bond to the neighboring chlo-
rine ligand (N(2)‚‚‚Cl(1) ) 3.064(11) Å, N(2)-H ) 0.91
Å, Cl(1)‚‚‚H ) 2.39 Å, N(2)-H‚‚‚Cl(1) ) 130°). The
carbene ligand shows negligible deviation from planar-
ity, and the dihedral angle between the carbene plane
and the coordination plane (87.79(49)°) is within the
range found for other platinum(II) carbene complexes.7

2436 Organometallics, Vol. 18, No. 13, 1999
Ferguson et al.
nich cation with anionic species 4e could involve elec-
trophilic attack at platinum (oxidative addition) to give
the platinum(IV) intermediate 27. Indeed, formation of
27 might proceed via direct 1,3-migration of the [NMe2-
CH2]+ fragment in intermediate 3e from nitrogen to
platinum. This would be more consistent with the
observed ineffectiveness of excess diamine in trapping
the Mannich cation27 or even in having a significant
retarding effect on the conversion of cyclic intermediate
2a into carbene complex 1a . Conversion of 27 into final
products, 25 and 1e, could involve net proton abstrac-
tion by one of the two -CH2NMe2 moieties in 27 from
the methylene group of the other and 1,2-elimination
of Me3N, respectively. Formation of carbene derivatives
by the latter type of mechanism is well-known for early
transition metals.28
A preferable alternative mode of decomposition of
intermediate 27 would involve an R-H shift to give the
Pt(IV) carbene hydride species 28.29 Formation of 1e
would then simply require reductive elimination of
Me3N, while 25 would result from elimination of HCl.
Analogous modes of reaction have been proposed by
others for various Pt(IV) complexes. Thus, decomposi-
tion of platina(IV)cyclobutane derivatives can proceed
via an initial R-H shift to the metal to give a Pt(IV)
carbene hydride species with subsequent reductive
elimination involving the hydride.30 An R-H shift from
the CH2NMe2 moiety may be particularly favorable,
since the resulting carbene species should be relatively
stable.31 Reductive elimination of HCl from Pt(IV)
complexes (and the reverse reaction) is well-known32
and believed often to entail removal (or addition) of H+
and Cl- in two separate steps. The observed increase
in the amount of 25 formed relative to 1e with increas-
ing excess of diamine could then be accounted for by an
increase in the rate of H+ abstraction from 28. It is
interesting that no product analogous to 25 has been
observed in the reactions involving phosphine ligands.
This might be rationalized by considering that inter-
mediates analogous to 28, but containing a phosphine
ligand instead of Ph3As, should be subject to readier
reductive elimination of Me3N due to the higher trans
effect of phosphines relative to arsines.
F igu r e 3. View of the cation of 26 with the numbering
scheme. Phenyl ring C atoms are labeled Ci1-Ci6 (i )
1-3). Thermal ellipsoids are drawn at the 30% probability
level. Only the major conformation found for the phenyl
groups is shown.
Sch em e 3
(b ) F r om (Dim et h yla m m on io)m et h yl Com p lex
21. A mechanism similar to that proposed in (a) above
can be envisaged for the conversion of 20 into carbene
complex 1a , viz. a 1,3-proton shift from N to Pt to
generate a Pt(IV) hydride intermediate,33 an R-H shift
from the resulting CH2NMe2 moiety to give a Pt(IV)
carbene dihydride, and reductive elimination of H2 to
give 1a . Alternatively, an R-H shift might precede
As expected, the Pt(1)-C(5) (carbene) bond (1.929(16)
Å) is shorter than the Pt(1)-C(1) (aminomethyl) bond
(2.053(10) Å), although the comparison is complicated
by the different trans ligands (Cl and As respectively).
The platinum-carbene distance is similar to that found
for 1a (1.96(1) Å),7 as are the trans Pt-Cl distances
(Pt(1)-Cl(1) ) 2.366(4) vs 2.347(3) Å in 1a ). The
considerable shortening of the C(5)-N(6) bond (1.24(2)
Å) compared to C(1)-N(2) (1.489(17) Å) reflects sub-
stantial double-bond character in the former, as found
also for 1a (carbene C-N ) 1.25(1) Å).
Mech a n ism of F or m a tion of Ca r ben e Com p lexes
1. (a ) F r om Cyclic Sp ecies 2. Possible mechanisms
of formation of 1e and 25 are outlined in Scheme 3.
Formation of simple carbene product 1e may proceed
in a manner similar to that suggested in Scheme 1 for
the Ph3P analogue. Alternatively, reaction of the Man-
(27) The possibility of liberating Mannich cation is indicated by the
formation of small amounts of 12/13(?)13 in the presence of excess
diamine, or upon TLC of the cyclic ylide complex 2a .
(28) Feldman, J .; Schrock, R. R. In Progress in Inorganic Chemistry;
Lippard, S. J ., Ed.; Wiley: New York, 1991; Vol. 39, pp 1-74.
(29) Complexes of this type, containing late transition metals in high
oxidation states, have been postulated as reactive intermediates in
several processes. See: Alias, F. M.; Poveda, M. L.; Sellin, M.;
Carmona, E. Organometallics 1998, 17, 4124-4126 and references
therein.
(30) (a) Puddephatt, R. J . Coord. Chem. Rev. 1980, 33, 149-194.
(b) J ennings, P. W.; J ohnson, L. L. Chem. Rev. 1994, 94, 2241-2290.
(31) Cf. formation of PtIVCHNMe2 complexes by oxidative addition
of [Me2NCHCl]Cl to Pt(II) precursors: Rendina, L. M.; Vittal, J . J .;
Puddephatt, R. J . Organometallics 1995, 14, 1030-1038.
(32) See e.g.: Hill, G. S.; Rendina, L. M.; Puddephatt, R. J .
Organometallics 1995, 14, 4966-4968 and references therein.

Formation of (Dimethylamino)carbene Complexes
Organometallics, Vol. 18, No. 13, 1999 2437
NMR (CDCl3, 100 MHz): δ 201.6 (1J Pt-C ) 1136 Hz), 50.96
(3J Pt-C ) 70 Hz), 48.40 (3J Pt-C ) 70 Hz). The more polar
fraction contained (trimethylammonio)methyl complex 11a
(163.2 mg, 0.271 mmol, 18.5% yield). Crystallization of this
material from dichloromethane/acetone (1:3) gave colorless
needles, one of which was selected for X-ray crystallographic
examination.
proton attack at Pt. Some precedent for such a pathway
is provided by the reported34 formation of a Pt(II)
alkoxycarbene hydride complex from a PtII[CH(Me)OEt]
precursor.
Exp er im en ta l Section
(b) When similar reactions were carried out in CHCl3
stabilized with 0.75% of EtOH, products 1a and 11a were
accompanied by a new species, 14 (see below), which is slightly
less polar than 11a .
Spectral data were acquired as follows: 1H and 13C NMR
spectra, Varian UNITY 400 or Gemini 200 (CDCl3 solution,
residual proton resonance at δ 7.24 and carbon resonance at
δ 77.0 as references); 31P NMR spectra, Varian UNITY 400
(CDCl3 solution unless indicated otherwise, phosphorus reso-
nance of triphenylphosphine in CDCl3 at δ -5.31 as external
(c) A solution of COD complex 5 (63.2 mg, 0.163 mmol), PPh3
(37.2 mg, 0.142 mmol), and Me2NCH2NMe2 (28.0 µL, 0.204
mmol) in freshly distilled chloroform (5 mL) was left for 4 h
at ambient temperature to allow partial buildup of 2a and then
subjected to preparative TLC. Three fractions were recovered.
The most polar (14.6 mg) was essentially pure 2a : that of
intermediate polarity (6.5 mg) also contained essentially a
single component which showed δP 8.41 (1J Pt-P ) 4144 Hz) and
1
reference). H NMR data required for the discussion and 31P
NMR data are collected in Tables 1 and 2, respectively. 13C
and additional 1H NMR data are given below. Elemental
analyses were determined by Guelph Chemical Laboratories
Ltd., Guelph, Ontario, Canada. Preparative-scale thin-layer
chromatography (TLC) was performed on Kieselgel G (Merck)
using MeOH/CH2Cl2 (3:97) as eluting solvent. Reactions were
carried out without precautions to exclude air or moisture
unless otherwise indicated.
3
δH 4.83 (2J Pt-H ) 56 Hz, J P-H ) 3.7 Hz, Pt-CH2) and 2.88 (s,
NMe2), suggesting a structure such as 12 or 13.13 The least
polar fraction (50.6 mg) consisted of a mixture from which
[(COD)PtCl2] (10.3 mg), hydride 15 (14.7 mg), the phos-
phine dimethylamine complex 19 (4.3 mg), and starting
complex 5 (7.6 mg) were recovered by further chromatography.
Upon standing in solution in CDCl3, the fraction of intermedi-
ate polarity slowly gave carbene complex 1a (10-15% over 4
days).
Crystal data and details of data collection, structure solu-
tion, and refinement are summarized in Table 4.
Rea ction s of [(COD)P t(CH2Cl)Cl] (5) w ith P P h 3 a n d
Me2NCH2NMe2. (i) NMR-Sca le Rea ction s in CDCl3 (0.75
m L). (a) A solution containing 5 (12.9 mg, 0.033 mmol), PPh3
(8.1 mg, 0.031 mmol), and Me2NCH2NMe2 (4.4 µL, 0.032 mmol)
was left at ambient temperature. Monitoring by 1H and 31P
NMR spectroscopy showed immediate formation of bis(phos-
phine) complex 7a and subsequent formation of cyclic ylide
complex 2a and then the final products carbene complex 1a
and (trimethylammonio)methyl complex 11a . The concentra-
tion of 2a reached a maximum after about 1 day, and complete
conversion to final products required about 10 days.
(d) COD complex 5 (162.0 mg, 0.417 mmol), PPh3 (101.0 mg,
0.380 mmol), and Me2NCH2NMe2 (70 µL, 0.51 mmol) were
dissolved in CH3CN (20 mL, freshly distilled from CaH2), and
the resulting solution was heated at 60-70 °C for 2.5 h.
Preparative TLC gave three major products: most polar, 11a
(42.9 mg); intermediate polarity, 1a (126.2 mg); least polar,
the new compound 24 (26.4 mg after crystallization from
dichloromethane/diethyl ether (1:3); crystal suitable for X-ray
structure determination). The Pt-CH2CH2- moiety shows δH
(b) When this experiment was repeated with heating at 60-
65 °C for 3 h, reaction to give 1a and 11a was complete but
the relative amount of the latter was greater (see (c) for a
similar experiment).
2
(200 MHz) 1.34 (apparent dt, J Pt-H ) 77 Hz) and 2.57
3
(apparent t, J Pt-H ) 52 Hz).
(e) A similar experiment performed in CD3CN gave the same
three products, but 24 now contained the -CH2CD2CONMe2
moiety (2D NMR resonance at δ 2.57).
(c) Three solutions were made up, each containing 5 (9.7
mg, 0.025 mmol) and PPh3 (6.6 mg, 0.025 mmol). Two
equivalents (7.0 µL) of Me2NCH2NMe2 was added to tube 1
and 8 equiv (28.0 µL) to each of tubes 2 and 3. The first two
were left at ambient temperature, and the last was heated at
65 °C for 4 h. Complete reaction for tubes 1 and 2 required a
time similar (ca. 10 days) to that found in experiment a. After
1 day, when cyclic intermediate 2a was the major complex
present, the 31P NMR spectrum of tube 2 showed, inter alia, a
weak signal at δ 8.41 corresponding to a (dimethylamino)-
methyl complex.13 After 10 days, tube 1 contained 1a , 11a ,
and 17 (relative peak heights in 31P NMR spectrum 7.7:1.8:1,
respectively) and tube 2 contained 1a , 17, 16, and 11a (6.1:
2.6:1:1). Reaction was complete in the heated tube, tube 3,
which contained 1a , 17, 16, and 11a (2.9:1.1:1:1).
(ii) P r ep a r a tive-Sca le Rea ction s. (a) COD complex 5
(570.4 mg, 1.47 mmol), PPh3 (385.4 mg, 1.47 mmol), and Me2-
NCH2NMe2 (0.50 mL, 3.6 mmol) were dissolved in CHCl3 (40
mL, freshly distilled from P2O5 under nitrogen), and the
resulting solution was heated at reflux for 2 h and then left
overnight at ambient temperature under nitrogen. Preparative
TLC gave two major fractions, the less polar of which contained
carbene complex 1a (536.9 mg, 0.917 mmol, 62.4% yield). 13C
Rea ction of Ca r ben e Com p lex 1a w ith P P h 3. Addition
of PPh3 (7.5 mg, 0.026 mmol) to a CDCl3 solution of carbene
complex 1a (12.3 mg, 0.021 mmol) gave trans-chloro[(dimethyl-
amino)methylene]bis(triphenylphosphine)platinum(II) chloride
(16), which was obtained as colorless needles (18.9 mg) upon
crystallization from dichloromethane/diethyl ether (1:3). A 1H
NMR spectrum of the crystalline material indicated the
presence of 1-2 equiv of water. Anal. Calcd for C39H37Cl2NP2-
Pt‚1.5H2O: C, 53.55; H, 4.61; N, 1.60. Found: C, 53.44; H,
4.63; N 1.61.
Rea ction of Ca r ben e Com p lex 1a w ith (Me2NH)2CO2.
Addition of an excess of the amine adduct to a CDCl3 solution
of carbene complex 1a resulted (1H and 31P NMR spectra) in
its rapid, and clean, conversion into the dimethylamine
complex 17. When this solution was evaporated in vacuo and
the residue redissolved in CDCl3, the NMR spectra indicated
the presence of both 1a and 17. Preparative TLC of this
mixture gave only 1a .
R ea ct ion of [(COD)P t (CH2Cl)Cl] (5) w it h P P h 3 a n d
Me2NCH2OEt. Me2NCH2OEt35 (4.6 µL, 0.033 mmol; contained
ca. 20% of Me2NCH2NMe2) was added to a solution of 5 (12.9
mg, 0.033 mmol) and PPh3 (8.2 mg, 0.031 mmol), in CDCl3.
Monitoring by 1H and 31P NMR spectroscopy showed, after the
initial generation of bis(phosphine) complex 7a , growth of
signals corresponding to cyclic intermediate 2a and products
1a , 11a , and 14. After 1 day, relative peak heights in the 31P
(33) Models for this 1,3-proton shift may be provided by the
N-H‚‚‚X-PtII (X ) Cl, Br) and N-H‚‚‚PtII species formed from certain
organoplatinum-amine complexes in the presence of HX. See: (a)
Wehman-Ooyevaar, I. C. M.; Grove, D. M.; de Vaal, P.; Dedieu, A.;
van Koten, G. Inorg. Chem. 1992, 31, 5484-5493. (b) Wehman-
Ooyevaar, I. C. M.; Grove, D. M.; Kooijman, H.; van der Sluis, P.; Spek,
A. L.; van Koten, G. J . Am. Chem. Soc. 1992, 114, 9916-9924.
(34) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1997, 119, 848-849.
(35) Heaney, H.; Papageorgiou, G.; Wilkins, R. F. J . Chem. Soc.,
Chem. Commun. 1988, 1161-1163.

2438 Organometallics, Vol. 18, No. 13, 1999
Ferguson et al.
NMR spectrum were 8.7:7.5:2.5:1 for 7a , 11a + 14, 2a , and
1a , respectively. After standing for a further 3 days, the
solution was heated at 55 °C for 8 h to drive the reaction to
completion. At this stage integration of the 1H NMR spectrum
indicated that the major products 1a , 11a , and 14 were present
in a ratio of ca. 3:2:4, respectively. cis-Dichloro[((ethoxymethyl)-
dimethylammonio)methyl](triphenylphosphine)platinum(II)
(14; 5.7 mg), was isolated by preparative TLC, as a band of
intermediate polarity between 1a and 11a , and purified by
crystallization from dichloromethane/hexane (1:3). Anal. Calcd
for C24H30Cl2NOPPt: C, 44.66; H, 4.68; N, 2.17. Found: C,
44.73; H, 4.74; N 2.10.
Rea ction s of [(COD)P t(CH2Cl)Cl] (5) w ith P P h 3 a n d
(Me2NH)2CO2. (i) COD complex 5 (11.9 mg, 0.031 mmol), PPh3
(8.1 mg, 0.031 mmol), and dimethylammonium dimethylcar-
bamate (2.3 mg, 0.017 mmol) were dissolved in 0.75 mL of
CDCl3. A 31P NMR spectrum, run after 1 h, showed two major
peaks assignable to 7a and 18: after 1 day, signals ascribable
to 1a , 2a , and 11a had appeared. The solution was left until
the signal from 18 (and 2a ) had disappeared (a further 9 days),
at which stage two further 31P signals, due to hydride complex
15 and trans-[(Ph3P)(Me2NH)PtCl2] (19), were present. Samples
of all four products, 1a , 11a , 15, and 19, were recovered by
preparative TLC.
A showed significant 31P signals corresponding to carbene
complex 1a , cis-[(Ph3P)2PtCl2], chelate complex 21, (dimethyl-
ammonio)methyl complex 20, and hydride 15. One day after
the addition of paraformaldehyde solution B gave strong
signals ascribable to cyclic ylide intermediate 2a , while after
12 days 31P signals corresponding mainly to 1a and ylide
complex 11a were observed.
(iv) A CDCl3 solution was prepared as for solution B in (iii).
After 3 h, when essentially all of the starting platinum complex
had been converted into 18, the solution was evaporated and
the residual gum was pumped for 6 h at 0.05 mmHg. The gum
was then redissolved in CDCl3. The major species present was
20, with the main byproducts being cyclic ylide complex 2a
and hydride 15. Upon standing for 7 days the signals corre-
sponding to 2a and 20 shrank while those for carbene complex
1a appeared and grew.
Rea ction s of [(COD)P t(CH2Cl)Cl] (5) a n d Me2NCH2NMe2
w ith (p-F C6H4)3P or (p-MeOC6H4)3P . NMR-scale reactions
of these two phosphines proceeded very similarly to that
described above for PPh3. Thus, immediately after mixing,
signals for the bis(phosphine) complexes 7b,c dominated the
31P NMR spectra. Over the next few hours, resonances due to
cyclic intermediates 2b,c appeared, followed by those from the
final products, carbene complexes 1b,c and (trimethylammo-
nio)methyl complexes 11b,c, with complete conversion requir-
ing more than 1 week. The intermediates were identified only
on the basis of their NMR spectra. The products, 1b,c and
11b,c, were isolated by preparative TLC. For comparison
purposes, 5 (0.033 mmol) was reacted with equimolar quanti-
ties of Me2NCH2NMe2 and each of PPh3, (p-FC6H4)3P, and (p-
MeOC6H4)3P. After 2 days at room temperature the solutions
were heated at 55 °C for 4 h to ensure that the decomposition
of cyclic intermediates was complete (31P NMR spectra).
Relative peak heights in the 31P NMR spectra at this stage
were 2.5:1, 1.7:1, and 4.2:1 for 1a :11a , 1b:11b, and 1c:11c,
respectively. Preparative TLC gave 1a (13.7 mg), 11a (4.2 mg),
1b (14.2 mg), 11b (4.3 mg), 1c (13.7 mg), and 11c (1.8 mg).
Crystals of cis-dichloro[(dimethylamino)methylene][tris(4-
methoxyphenyl)phosphine]platinum(II) (1b) obtained from
dichloromethane/hexane contained (1H NMR) 0.5-1 mol equiv
of dichloromethane. Anal. Calcd for C24H28Cl2NO3PPt‚0.75CH2-
Cl2: C, 40.22; H, 4.02; N, 1.89. Found: C, 40.15; H, 4.11; N,
1.87. cis-Dichloro[(dimethylamino)methylene][tris(4-fluoro-
phenyl)phosphine]platinum(II) (1c), obtained similarly, also
contained dichloromethane. Anal. Calcd for C21H19Cl2F3NPPt‚
0.1CH2Cl2: C, 39.12; H, 2.99; N, 2.16. Found: C, 38.97; H,
3.06; N, 1.97.
(ii) The previous reaction was repeated on a larger scale (5
(45.3 mg), PPh3 (31.0 mg), and the amine adduct (11.4 mg) in
2 mL of CDCl3). After 5 h, when the solution contained (31P
NMR spectrum) mainly the dimethylamine complex 18, it was
added dropwise to hexane (30 mL) in an attempt to precipitate
18.
A
31P NMR spectrum of the precipitate (23 mg) showed no
signal corresponding to 18, but rather two major signals at δ
15.21 (1J Pt-P ) 4564 Hz) and 6.1 (1J Pt-P ) 3985 Hz). Prepara-
tive TLC of this material gave a fraction which contained
largely the major component (20, δP 15.21), while the other
1
main component decomposed on the plates. H NMR and 31P
NMR spectra of the TLC fraction showed relatively weak
signals ascribable to carbene complex 1a in addition to those
of 20 (δH 2.63 (6H, d, J ) 5.6 Hz, NMe2), 2.70 (2H, m, CH2N),
7.25-7.80 (15H, aromatic H), 8.1 (1H, br, NH)). Spectra run
subsequently, over several days, showed a steady increase in
the strength of the signals for 1a relative to those for 20, with
complete conversion requiring more than 1 week at ambient
temperature.
The filtrate was evaporated in vacuo to give a white residue
(51 mg), the 31P NMR spectrum of which showed a major signal
corresponding to 18 and minor signals for bis(phosphine)
complex 7a and hydride 15. When this solution was allowed
to stand at ambient temperature for 3 days, the signal for 18
disappeared and was replaced mainly by signals at δ 14.25
(21) and 6.1 (1J Pt-P ) 3985 Hz) (cf. precipitate). Preparative
TLC of this mixture gave 21 (19 mg) as the only isolable
product, the other major component decomposing on the plate.
Crystallization of 21 from dichloromethane/hexane gave an
analytical sample (δC 92.67 (J Pt-C ) 26 Hz, J P-C ) 3.2 Hz),
66.88 (J Pt-C ) 800 Hz, J P-C ) 3.2 Hz), 45.33 (J P-C ) 2.4 Hz)).
Anal. Calcd for C22H25ClNOPPt: C, 45.48; H, 4.34; N, 2.41.
Found: C, 45.13; H, 4.40; N, 2.27.
Reaction of [(COD)P t(CH2Cl)Cl] (5) with tr a n s-[(Et3P )2-
P t(CH2Cl)Cl] (7d ) a n d Me2NCH2NMe2. No reaction was
observed (1H NMR spectra) when a solution of 5 (10.7 mg,
0.028 mmol), 7d (12.6 mg, 0.024 mmol), and diamine (6.8 µL,
0.050 mmol) was kept at room temperature for 3 days. The
solution was then heated to 55 °C. After 1 day, the reaction
appeared to be complete and peaks for two major species, 1d
1
and 11d , were evident in the H NMR spectrum. Preparative
TLC gave 1d (8.2 mg) and 11d (4.8 mg). Crystallization of 1d
from chloroform gave white needles. Anal. Calcd for C9H22Cl2-
NPPt: C, 24.50; H, 5.03; N, 3.17. Found: C, 24.57; H, 5.06;
N, 3.04.
(iii) Two CDCl3 solutions were prepared, each containing 5
(9.7 mg, 0.025 mmol) and PPh3 (6.6 mg, 0.025 mmol). One
(solution A) or two (solution B) equivalents of dimethylamine
(as the CO2 adduct) was added to these solutions. After 3 h at
Rea ction s of [(COD)P t(CH2Cl)Cl] (5) w ith AsP h 3 a n d
Me2NCH2NMe2. (i) When 5 (8.5 mg, 0.022 mmol), AsPh3 (6.7
mg, 0.022 mmol), and diamine (3.1 µL, 0.023 mmol) were
dissolved in CDCl3, bis(arsine) complex 7e was formed rapidly.
Upon standing at ambient temperature, resonances for the
cyclic species 2e appeared in the 1H NMR spectrum, with
complete conversion requiring about 1 day. Since no further
reaction was apparent during the next 2 days, the solution
was heated at 55 °C for 6 h, after which time the signals
arising from 2e were replaced by those for carbene complexes
1e and 25. Preparative TLC gave 1e (3.8 mg) and 25 (5.0 mg).
Crystallization of the former from dichloromethane/hexane
1
ambient temperature H and 31P NMR spectra indicated that
chloromethyl dimethylamine complex 18 was the major plati-
num-containing species present in both solutions. Solution A
also contained small amounts of COD complex 5 and bis-
(phosphine) complex 7a , while solution B contained no more
than traces of these complexes. Excess solid paraformaldehyde
(2 mg) was added to each solution, and the mixtures were
shaken at intervals and monitored by 1H and 31P NMR
spectroscopy over a period of 12 days. After this time solution

Formation of (Dimethylamino)carbene Complexes
Organometallics, Vol. 18, No. 13, 1999 2439
gave cis-dichloro[(dimethylamino)methylene](triphenylarsine)-
platinum(II) (1e). Anal. Calcd for C21H22AsCl2NPt: C, 40.08;
H, 3.52; N, 2.23. Found: C, 39.96; H, 3.72; N, 2.14. A solution
of 25 in CH2Cl2 was shaken with excess KPF6 in H2O to give
26, which was recovered from the organic layer and crystal-
lized from CHCl3/hexane (3/1). This provided crystals suitable
for X-ray analysis. 13C NMR (CDCl3, 100 MHz): δ 203.74
(1J Pt-C ) 1243 Hz), 50.79 (3J Pt-C ) 80 Hz), 48.55 (3J Pt-C ) 100
Hz), 46.89 (3J Pt-C ) 40 Hz) and 44.01 (1J Pt-C ) 791 Hz).
(ii) When the reaction outlined in (i) was repeated (0.025
mmol scale) but with heating at 55 °C from the outset,
complete decomposition of cyclic intermediate 2e required ca.
10 h. Preparative TLC gave carbene complex 1e (8.0 mg) and
the more polar (trimethylammonio)methyl complex 11e (6.2
mg) as the major products.
with acetone (1.5 mL) to give a solution from which crystalline
material began to deposit almost immediately. After standing
overnight, the supernatant was removed and the crystals were
washed successively with acetone, diethyl ether, and pentane
and dried in vacuo. This gave essentially pure trans(C,Cl)-
chloro[(dimethyl((dimethylamino)methyl)ammonio))methyl-
C,N](triphenylarsine)platinum(II) chloride (21.9 mg). Anal.
Calcd for C24H31AsCl2N2Pt: C, 41.87; H, 4.54; N, 4.07. Found:
C, 41.57; H, 4.72; N, 3.85.
Reaction of tr a n s-[(P h 3As)2P t(CH2Cl)Cl] with Me2NCH2-
NMe2. The bis(arsine) 7e was obtained by reaction of 5 (19.4
mg, 0.050 mmol) with Ph3As (32.3 mg, 0.105 mmol) in CH2-
Cl2. Crystallization from CH2Cl2/pentane (1:3) gave feathery
crystals of trans-bis(triphenylarsine)chloro(chloromethyl)-
platinum(II) (7e; 43.0 mg). Anal. Calcd for C37H32As2Cl2Pt: C,
49.79; H, 3.61. Found: C, 49.88; H, 3.74. Monitoring of a CDCl3
solution of 7e (8.9 mg, 0.010 mmol) and diamine (2.0 µL, 0.014
mmol) by 1H NMR showed the development of resonances
arising from cyclic species 2e. Complete conversion required
1-2 days.
(iii) Reaction i was also repeated (0.033 mmol scale) using
C6D6 as solvent. As before, essentially complete conversion into
2e was observed within 24 h, although some of this product
deposited as a gum.
(iv) A series of four reactions was carried out in CDCl3 on a
0.025 mmol scale (in 5 and arsine) but using 2, 4, 8, and 16
equiv of diamine, and formation of cyclic product 2e was
monitored. Reaction took place at essentially the same rate
in all four samples. After standing for 2 days, to ensure that
formation of 2e was complete, the samples were heated at 60
°C for 6 h to promote its decomposition. Monitoring by 1H NMR
spectroscopy showed the formation of the two carbene com-
plexes 1e and 25 and indicated that the relative amount of
the former decreases with increasing diamine concentration.
(v) Reaction i was carried out on a 0.050 mmol scale, and
after 1 day, when formation of 2e was complete, the solvent
was evaporated in vacuo. The resulting gum was triturated
Ack n ow led gm en t. We thank NSERC of Canada for
financial support and Ms. Valerie Robinson for perform-
ing the 2-D NMR experiments.
Su p p or tin g In for m a tion Ava ila ble: Lists of fractional
coordinates, calculated hydrogen coordinates, anisotropic ther-
mal parameters, and interatomic distances and angles for 11a ,
24, and 26. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM990049H