Reversible CO exchange at platinum(0). An example of similar complex properties produced by ligands with very different stereoelectronic characteristics

Abstract

The ligands 1,2-C₆H₄(CH₂P^tBu₂)₂ (L_a) and 1,2-C₆H₄(P^tBu₂)(CH₂P^tBu₂) (L_b) displace norbornene (nbe) from [Pt(η²-nbe)₃] to give [PtL(η²-nbe)] where L = L_a (1a) or L_b (1b); 1a is fluxional on the NMR timescale. Reaction of 1a,b with CO gives the corresponding monocarbonyls [PtL(CO)] where L = L_a (2a) or L_b (2b) which then react further, and reversibly, to give the dicarbonyls [PtL(CO)₂] where L = L_a (3a) or L_b (3b). The CO interchange between 2a,b and 3a,b is compared with the only other such system (2f and 3f), which are complexes of (C₂F₅)₂PCH₂CH₂P(C₂F₅)₂ (L_f). Ethene reacts smoothly with 2a to give (4a) and H₂ with 2a generates some [PtH₂(L_a)]. Protonation of 2a gives [Pt(L_a)(H)(CO)][B(C₆F₅)₄] (5a) whose crystal structure has been determined. Similarly protonation of 2b gives [Pt(L_b)(H)(CO)][B(C₆F₅)₄] as a mixture of geometric isomers 5b–6b.