Phospha-alkyne hydro-osmiation: Synthesis of [Os{κ1P,κ1P'-P=CRP(=CHR)}Cl(CO)(PPh3)2] (R = CMe3)

Article abstract of DOI:10.1039/a900257j

The reaction of [OsHCl(CO)(PPh₃)₂(BTD)] (BTD = 2,1,3-benzothiadiazole) with P≡CCMe₃ provides the novel complex [Os(κ¹P,κ¹P'-P=CRP(=CHR)Cl(CO)(PPh₃)₂] (R = CMe₃) which

Full text of DOI:10.1039/a900257j

Phospha-alkyne hydro-osmiation: synthesis of
1
1
[Os{k P,k PA-PNCRP(NCHR)}Cl(CO)(PPh3)2] (R = CMe3)
Anthony F. Hill,*a Cameron Jones*b and James D. E. T. Wilton-Elya
a Centre for Chemical Synthesis, Department of Chemistry, Imperial College of Science Technology and Medicine,
South Kensington, London, UK SW7 2AY. E-mail: a.hill@ic.ac.uk
b Department of Chemistry, Cardiff University, Cardiff, UK CF1 3TB. E-mail: jonesca6@cardiff.ac.uk
Received (in Cambridge, UK) 8th January 1999, Accepted 20th January 1999
The reaction of [OsHCl(CO)(PPh3)2(BTD)] (BTD
=
spectroscopic and microanalytical data,† amongst which the 31
P
2,1,3-benzothiadiazole) with P·CCMe3 provides the novel
NMR data are particularly informative. The phospha-alkenyl
ligand gives rise to a triplet resonance at d 462.7 [J(P2P) 13.1
Hz] due to coupling to the two chemically equivalent phosphine
phosphorus nuclei. This resonance is shifted slightly to higher
field of that for 2a [d 450.4, J(P2P) 10.0 Hz]. Whilst 2a is air
stable both as a solid and in solution, solutions of the more
electron rich complex 2c are rapidly decomposed by air.
The reaction of 3a with P·CCMe3 was then investigated and
surprisingly ultimately found not to provide the analogous
phospha-alkenyl complex [Os(PNCHCMe3)Cl(CO)(PPh3)2].
Rather, the product 4 obtained after 18 h at room temperature
was found to incorporate two equivalents of phospha-alkyne.
Even when the reaction was performed with a deficiency of
phospha-alkyne, no species other than 3a and 4 could be
spectroscopically observed to accumulate during the course
of the reaction. In the absence of crystals suitable for an
X-ray diffraction study, the complex 4 is formulated as the
1
1
complex [Os{k P,k PA-PNCRP(NCHR)Cl(CO)(PPh3)2] (R =
CMe3) which features both phospha-alkenyl and phospha-
alkene donors within the same metallacycle.
We have recently described the facile hydroruthenation of
phospha-alkynes by the ruthenium complexes [RuHCl-
(CA)(PPh3)3] (A = O 1a, S 1b).1 The phospha-alkenyl
complexes [Ru(PNCHCMe3)Cl(CA)(PPh3)2] (A = O 2a, S 2b)
which results are remarkable for a number of reasons. Firstly,
the metal centre is coordinatively unsaturated, as a result of a
non-linear Ru–P–C phospha-alkenyl spine. Secondly, the
phospha-alkenyl ligand is unusually simple, in that it lacks the
previously requisite kinetic or thermodynamic stabilisation
conferred by bulky or p-dative substituents.2 Finally but
perhaps most significantly, the phospha-alkenyl ligand serves
as a versatile precursor for the preparation of a range of novel
complexes of otherwise inaccessible organophosphorus ligands
including the unusual phospha-alkenes XPNCHCMe3 (X = H,
Me, ClHg, AuPPh3, HgPh).3 The successful synthesis and
synthetic utility of the complexes 2a and 2b immediately raises
the question of the generality of the phospha-alkyne hydro-
metallation strategy. Encouragingly, Nixon and coworkers have
recently reported the hydrozirconation of a coordinated phos-
pha-alkyne by the Schwarz’ reagent to provide a synthetically
useful P-zirconated phospha-alkene complex [ZrPt(m-
PCHCMe3)Cl(dppe)(h-C5H5)2].4 Furthermore the hydrostan-
nylation of phospha-alkynes has now been reported, although in
this case the process lacks the regioselectivity offered by the
two transition metal systems.5 Herein we report the hydro-
osmiation of a phospha-alkyne, leading to a novel osmacycle
which includes both phospha-alkene and phospha-alkenyl
donor components.
metallacyclic
phospha-alkenyl–phospha-alkene
complex
In contrast to the ruthenium complexes 2a and 2b, treating
[OsHCl(CO)(PPh3)3] 1c with an excess of P·CCMe3 fails to
result in any appreciable reaction. We have encountered a
similar lack of reactivity of 1c towards alkynes and attributed
this to the lack of phosphine lability under mild conditions.
However, prior conversion of 1c to the more labile complex
[OsHCl(CO)(PPh3)2(BTD)] 3a (BTD = 2,1,3-benzothiadia-
zole) provides a reagent capable of alkyne hydro-osmiation
under ambient conditions providing convenient access to the
complexes [Os(CHNCHR)Cl(CO)(PPh3)2(BTD)].6 It is note-
worthy that whilst the analogous ruthenium complex [RuHCl-
(CO)(PPh3)2(BTD)] 3b7 also hydrometallates alkynes to pro-
vide
coordinatively
saturated
s-alkenyl
complexes
[Ru(CHNCHR)Cl(CO)(PPh3)2(BTD)],8 we find that treating 3b
with an excess of P·CCMe3 results in the exclusive formation
of coordinatively unsaturated 2a with no indication of BTD
coordination. In a similar manner the acetonitrile complex
[RuHI(CO)(NCMe)(PPh3)2] reacts with P·CCMe3 to provide
the new phospha-alkenyl complex [Ru(PNCHCMe3)I-
(CO)(PPh3)2] 2c which despite being coordinatively un-
saturated, fails to recoordinate the liberated acetonitrile ligand
(Scheme 1). The formulation of 2c follows unambiguously from
Scheme 1
Chem. Commun., 1999, 451–452
451

1660, 1247, 1157, 1119, 968, 862, 849 cm21. NMR (CDCl3, 25 °C): 1H, d
0.90 [d, 9H, CH3, J(HP) 1.32 Hz], 6.41 [dt, 1H, PCH, J(HP) 4.48 J(HP2)
0.75 Hz], 7.32–7.68 (m, 30H, PPh). 31P{1H}, d 462.7 [t, PNC, 1 P, J(P2P) 13
Hz], 33.1 [d, 2 P, PPh3, J(PP2) 14 Hz]. FABMS: m/z (%) = 883 (2) [M]+,
853 (3) [M 2 CO]+, 781 (19) [M 2 PCHCMe3]+, 755 (6) [M 2 I]+, 654 (15)
[M 2 I 2 PCHCMe3]+, 625 (14) [M 2 CO 2 I 2 PCHCMe3]+. 4: IR
(CH2Cl2): 1940 [n(CO)] cm21. (Nujol): 1934 [n(CO)], 1718, 1311, 1263,
1089vs, 971, 931, 852 cm21. NMR (CDCl3, 25 °C): 1H, d 0.70, 0.90 (s 3
2, 9H 3 2, CH3), 6.83 [br d, 1H, PCH, J(PH) 12.6 Hz], 7.33, 7.66 (m 3 2,
30H, Ph]. 31P{1H}, d 578.9 (br s, 1 P), 111.9 [t, 1 P, J(PP) 19], 21.35 [dd,
2 P, J(PP) 12, 18 Hz] 13C{1H}: 226.1 [br d, PNCHR, J(PC) 68.0], 185.7 (m,
OsCO), 134.6 [t, C3,5 of Ph, J(P2C) 4.4], 133.3 [t, C1 of Ph, J(P2C) 25.9],
129.9 (s, C4 of Ph) 127.8 [t, C2,6 of Ph, J(P2C) 4.9], 48.0 (br s, P2CCMe3),
36.0 [d, CHCMe3, J(PC) 4.3], 30.5 [d, CH3, J(PC) 11.9 Hz], 29.8 (br s CH3).
NB: the neopentylidyne carbon resonance was not unambiguously identi-
fied and possibly lies beneath the phosphine resonances. FABMS: m/z (%)
= 999 (7) [M + H2O]+, 979 (1) [M]+, 779 (3) [M 2 PCHCMe3]+, 737 (6)
[M + H2O 2 PPh3]+, 707 (2) [M + H2O 2 CO 2 PPh3]+.
1
1
[Os{k P,k PA-PNC(CMe3)P(NCHCMe3)}Cl(CO)(PPh3)2] on
the basis of spectroscopic, micro-analytical and FABMS data.†
Characteristic data pertaining to the ‘OsCl(CO)(PPh3)2’ unit are
unremarkable, with interest focusing on those associated with
the novel metallacycle: Two But chemical environments follow
from the appearance of two singlet resonances in the 1H NMR
spectrum (d 0.90, 0.70) in addition to a doublet resonance at d
6.83 [2J(PH) 12.6 Hz] corresponding to the vinylic (neopentyli-
dene) proton. The 31P NMR spectrum consists of three
resonances: the two phosphine ligands give rise to a double-
doublet resonance [d 21.35, J(PP) 12, 18 Hz] confirming their
mutually trans disposition, straddling the molecular symmetry
plane; the phospha-alkenyl resonance appears as a slightly
broadened singlet at d 578.9 whilst the phospha-alkene
phosphorus nucleus is manifest as an apparent triplet at d 111.9
[J(PP) 19 Hz], indicating that the net coupling between the two
phosphorus nuclei of the metallacycle is negligible. Only one
isomer is formed with respect to the osmium stereochemistry,
and since our recent structural studies of various s-P phospha-
alkene complexes suggest a moderate p-acidity,3 it seems
reasonable that it is the isomer shown (phospha-alkene trans to
p-basic chloride) which is formed.
1 R. B. Bedford, A. F. Hill and C. Jones, Angew. Chem., Int. Ed. Engl.,
1996, 35, 547; R. B. Bedford, A. F. Hill, C. Jones, A. J. P. White, D. J.
Williams and J. D. E. T. Wilton-Ely, Organometallics, 1998, 17,
4744.
The metallacycle in 4 is unique in possessing both phospha-
alkenyl and phospha-alkene ligating groups, although other
metallacyclic phospha-alkenyl complexes have been reported,
2 For a recent review on the chemistry of phospha-alkenyl complexes,
see: L. Weber, Angew. Chem., Int. Ed. Engl., 1996, 35, 271.
3 R. B. Bedford, D. E. Hibbs, A. F. Hill, M. B. Hursthouse, K. M. A.
Malik and C. Jones, Chem. Commun., 1996, 1895; R. B. Bedford, A. F.
Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely,
J. Chem. Soc., Dalton Trans., 1997, 139, 1113; R. B. Bedford, A. F. Hill,
C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely,
Chem. Commun., 1997, 179; A. F. Hill, C. Jones, A. J. P. White, D. J.
Williams and J. D. E. T. Wilton-Ely, J. Chem. Soc., Dalton Trans., 1998,
1419.
4 M. H. A. Benvenutti, N. Cebac and J. Nixon, Chem. Commun., 1997,
1327.
5 M. Schmidz, R. Go¨ller, U. Bergstra¨ßer, S. Leininger and M. Regitz, Eur.
J. Inorg. Chem., 1998, 227.
6 A. F. Hill and J. D. E. T. Wilton-Ely, J. Chem. Soc., Dalton Trans.,
1998, 3501.
7 N. W. Alcock, A. F. Hill and M. S. Roe, J. Chem. Soc., Dalton Trans.,
1990, 1737.
viz.
[Os{PNC(CF3)O}(CO)2(PPh3)2],9
[Rh{PNC(CMe3)-
CNCH2}Cl(PPri3)2],10 and the l -phospha-alkenyl complex
[Ru{P(NO)NC(CMe3)C(NO)}(CNCMe3)2(PPh3)2],11 (spectro-
scopic data of which support our formulation). The route by
which 4 is formed presumably involves a slow insertion of one
equivalent of P·CCMe3 into the osmium hydride bond to
provide transiently the phospha-alkenyl complex [Os(PNCHC-
Me3)Cl(CO)(PPh3)2], followed by a rapid insertion of a second
equivalent of phospha-alkyne into the Os–P bond and sub-
sequent metallacyclisation. It is therefore noteworthy that
treating the ruthenium complexes 2a or 2c with an excess of
phospha-alkyne fails to result in any discernible reaction. Thus
our very modest attempt to generalise what appears a simple
reaction, phospha-alkyne hydrometallation, has highlighted the
diversity of reactivity available to phospha-alkynes through
coordinative activation by transition metals.
5
8 M. C. J. Harris and A. F. Hill, J. Organomet. Chem., 1992, 438, 209;
M. C. J. Harris and A. F. Hill, Organometallics, 1991, 10, 3903.
9 D. S. Bohle, G. R. Clark, C. E. F. Rickard and W. R. Roper,
J. Organomet. Chem., 1988, 353, 355; D. S. Bohle, C. E. F. Rickard and
W. R. Roper, J. Chem. Soc., Chem. Commun., 1985, 1594.
10 P. Binger, J. Haas, A. T. Herrmann, F. Langhauser and C. Kru¨ger,
Angew. Chem., Int. Ed. Engl., 1991, 30, 310.
A. F. H. gratefully acknowledges the Leverhulme Trust and
the Royal Society for the award of a Senior Research
Fellowship. Osmium and ruthenium salts were generously
provided by Johnson Matthey Chemicals Ltd.
11 A. F. Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-
Ely, Chem. Commun., 1998, 367.
Notes and references
† Selected data for new complexes. Satisfactory elemental microanalytical
data obtained. 2c: IR(CH2Cl2): 1936 [n(CO)] cm21. (Nujol): 1925 [n(CO)],
Communication 9/00257J
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Chem. Commun., 1999, 451–452