Chemistry of the metal carbonyls. Part 77. Some reactions of the platinumtriosmium complexes [Os3Pt(µ-H)2(CO)10(PR3)] with donor molecules; X-ray crystal structures of [Os3Pt(µ-H)2(CO)10(PPh3)2] and [OsPt2(CO)5(PPh3)2(µ3-MeC2Me)]

Abstract

The compounds [Os₃Pt(µ-H)₂(CO)₁₀(PR₃)] react with CO, PPh₃, or AsPh₃ to give complexes [Os₃Pt(µ-H)₂(CO)₁₀(PR₃)L][PR₃= P(cyclo-C₆H₁₁)₃, L = CO; PR₃= PPh₃ or AsPh₃]. Hydrogen-1 and ³¹P n.m.r. data for the compounds are discussed, and a single-crystal X-ray diffraction study has been carried out on the compound [Os₃Pt(µ-H)₂(CO)₁₀(PPh₃)₂], crystals of which are triclinic, space group P1, Z= 2, in a unit cell with lattice parameters a= 14.427(7), b= 12.793(5), c= 14.151(6)Å, α= 92.33(3), β= 120.87(3), and γ= 91.06(4)°. The structure has been refined to R 0.041 (R′ 0.044) for 5 794 independent reflections (2.9 ⩽ 2θ⩽ 60°, Mo-K_αX-radiation) collected at 200 K. The four metal atoms adopt a butterfly arrangement in contrast to the tetrahedral cluster structure of the 58-electron precursors [Os₃Pt(µ-H)₂(CO)₁₀(PR₃)]. In [Os₃Pt(µ-H)₂(CO)₁₀(PPh₃)₂] the metal–metal bonding distances are Os–Pt 2.717(1) and 2.848(1)Å, and Os–Os 2.773(1), 2.914(1), and 3.043(1)Å. Evidence is presented for the two hydrido-ligands bridging the longer Os–Pt and Os–Os bonds. One triphenylphosphine ligand is attached to platinum and the other to osmium, and all the carbonyl ligands are terminally bound. Reaction of [Os₃Pt(µ-H)₂(CO)₁₀(PPh₃)] with but-2-yne affords a mixture, from which five polynuclear metal complexes were isolated and studied by i.r. and n.m.r. spectroscopy. None of these products contained the Os₃Pt cluster of the precursor. One of the complexes was characterised as [OsPt₂(CO)₅(PPh₃)₂(µ₃-MeC₂Me)] and its structure established by X-ray diffraction. Crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell of dimensions a= 11.143(8), b= 17.458(12), c= 23.443(15)Å, and β= 113.82(5)°. The structure has been refined to R 0.031 (R′ 0.033) for 4 438 independent reflections (2.9 ⩽ 2θ⩽ 55°, Mo-K_αX-radiation) collected at 200 K. The metal atoms form an isosceles triangle [Os–Pt 2.662(2)(mean), Pt–Pt 3.033(2)Å] bridged by a face-bonding but-2-yne molecule whose orientation with respect to the triangle is µ₃(η²-‖). The osmium atom carries three terminal CO ligands, and each platinum a CO and PPh₃ group such that there is a cisoid arrangement OCPtPtCO; the Pt–Pt separation of 3.033(2)Å, however, suggests that there may be little direct metal–metal interaction.