Polyhedron p. 1175 - 1190 (1996)
Update date:2022-08-04
Topics:
Deeming, Antony J.
Doherty, Simon
Reaction of the chiral anionic ligand [Mo(CO)5(PPhH)]- with [PtCl2(L-L)] affords the neutral trimetallic monophosphido bridged complexes [Pt(μ-PPhH)2{Mo-(CO)5}2(L-L)] (L-L = dppe, Ph2PCH2CH2PPh2, 2; dpae, Ph2AsCH2CH2AsPh2, 3; dppe′, cis-Ph2PCH=CHPPh2, 4). Compounds 2-4 are the first examples of heterometallic complexes that contain two chiral primary phosphido bridges existing as pairs of diastereoisomers. [Pt(μ-PPhH)2{Mo(CO)5}2(dppe)] (2) has been characterized spectroscopically and by a single-crystal X-ray analysis. The molecular structure of 2 can be considered either as Mo2Pt phosphido-bridged trimer or a square-planar PtII complex bonded to one chelating dppe and two anionic phosphine ligands. The latter PtP4 description successfully accounts for the line broadening observed in the 31P{1H} NMR spectra of 2-4, which can be understood in terms of the existence of several interconverting rotameric forms arising from restricted rotation about the Pt-phosphido bond. The Pt - P - Mo angles of 122.1(1) and 123.5(1)° are some of the largest ever to be reported for phosphido-bridged heterometallics, reflecting the long Pt - Mo separations [4.349(2) and 4.320(2) A] and the electronic and structural flexibility of the phosphido bridge. The PtMo compound [Pt(μ-PPhH)2{Mo-(CO)4}(dppe)] (5), comprised of one neutral and one dianionic chelate ligand, was prepared from [Li]2[Mo(CO)5(PPhH)2] and [PtCl2(dppe)] and was shown to contain a conformationally rigid PtP4 structure with characteristically sharp 31P resonances. The 31P{1H} NMR spectrum of 5 is rich with information analysing as two overlapping AA′XX′ spin systems together with their AA′XX′M (M = 195Pt) counterparts. The values of 2J(P - P) and 1J(195Pt - P) are significantly lower for PPhH{Mo(CO)5}- than dppe, a difference that cannot be accounted for solely on the basis of bond length variations. Meso-[Pt(μ-PPhH)2{Mo(CO)5}2(dppe)] (2) is thermodynamically unstable, undergoing a rapid intramolecular elimination of [Mo(CO)6] to generate [Pt(μ-PPhH)2{Mo(CO)4}(dppe)] (5), while its racemic diastereoisomer, that which was observed in the crystal, decomposes to unidentified phosphorus-containing products.
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