Transition-metal hydrides and carbonyl anions as ligands toward a Pt centre in rhenium-platinum triangular clusters: A qualitative order of 'thermodynamic nucleophilicity'

Six novel mixed-metal spiked-triangle complexes [Re2Pt(μ-H)2(CO)9X] have been obtained. The metallo-ligands X bound to the Pt vertex are either transition-metal hydrides, such as HMn(CO)5, HRe(CO)4(PPh3), HRe(CO)3(PPh3)2, or carbonyl anions, such as [Mn(CO)5]-, [WCp(CO)3]- and [Co(CO)4]-. Two main synthetic routes have been used to prepare these complexes: (i) replacement of the labile ligand 1,5-cyclooctadiene (COD) of [Re2Pt(μ-H)2(CO)8(COD)] with CO and X; (ii) substitution of the labile 'ligand' HRe(CO)5 in [Re2Pt(μ-H)2(CO)9HRe(CO)5] by the ligands X. The neutral species [Re2PtMn(μ-H)3(CO)14] has been obtained by protonation of [Re2Pt(μ-H)2(CO)9Mn(CO)5] -. Variable temperature 1H NMR investigations showed that it exists in solution as two isomers a and b, likely differing in the location of one hydride, a having the structure [Re2Pt(μ-H)2(CO)9HMn(CO)5], and b the structure [Re2Pt(μ-H)3(CO)9Mn(CO)5]. The ligand HMn(CO)5 of a shows a high lability, being in fast exchange with free [HMn(CO)5] even at 193 K. At higher temperature interconversion between the two isomers and exchange between the hydrides bound to Pt in b is observed. The treatment of [Re2Pt(μ-H)2(CO)9WCp(CO)3] - with strong acids failed to give the protonated derivative. The strong nucleophile [FeCp(CO)2]- reacted with [Re2Pt(μ-H)2(CO)9HRe(CO)5] as a Broënsted base rather than as a nucleophile, giving deprotonation instead of substitution of the labile HRe(CO)5 ligand bound to Pt. The complex [Re2Pt(μ-H)2(CO)9HRe(CO) 4(PPh3)] has been characterised by X-ray single crystal analysis. It crystallises in the monoclinic space group P21/c (No. 14) with a=9.229(3), b=30.700(8), c=12.915(3) Å, β=98.05(2)°, V=3623(2) Å3 and Z=4. A series of displacement reactions of the type [Re2Pt(μ-H)2(CO)9X]+X′ ⇔ [Re2Pt(μ-H)2(CO)9(X′)] + X allowed the following qualitative order of affinity of the metallo-ligands X for the Pt atom (a scale of 'thermodynamic nucleophilicity') to be established: [Re(CO)5]- > [HRe2(CO)9]-≈[Mn(CO)5] ->[WCp(CO)3]->[Co(CO)4] -> [HRe(CO)4(PPh3)]>[HRe(CO)3(PPh 3)2]>[HRe(CO)5]>[HMn(CO) 5]>[HWCp(CO)3].