Alkyne or alkene binding versus hydrogenation in reactions with [Ir2H(CO)2(μ-H)2(Ph2PCH 2PPh2)2] [BF4]. Structure of [Ir2(C2H4)(CO)2(μ-H)(Ph 2PCH2PPh2)2] [BF4]

Article abstract of DOI:10.1016/s0020-1693(97)05464-9

The reactions of [Ir₂H(CO)₂(μ-H)₂(dppm)₂] [BF₄] (1) (dppm = Ph₂PCH₂PPh₂) with the alkynes, dimethyl acetylenedicarboxylate, hexafluoro-2-butyne or acetylene yield the respective products [Ir₂(H)₂(CO)₂(μ-H)(μ-RCCR)(dppm) ₂] [BF₄] (R = CO₂Me, CF₃, H) in which the alkyne bridges the metals, bound in a parallel orientation. With tetrafluoroethylene the analogous olefin-bridged product [Ir₂(H)₂(CO)₂(μ-H)(μ-C₂F ₄)(dppm)₂] [BF₄] is obtained. The reactions of 1 with diphenylacetylene or ethylene result in hydrogenation, to yield cis-stilbene and ethane, respectively, with subsequent reaction of the resulting unsaturated intermediate with additional substrate to give [Ir₂(CO)₂(μ-H)(μ-PhCCPh)(dppm)₂] [BF₄] or [Ir₂(C₂H₄)(CO)₂(μ-H)(dppm) ₂] [BF₄]. In the diphenylacetylene adduct this group is bound in a parallel position bridging the metals whereas the ethylene ligand binds to one metal in a terminal position opposite the Ir-Ir bond. The structure of this ethylene adduct has been determined by X-ray crystallography. This compound crystallizes in the monoclinic space group P2₁/n, having a = 13.6872(7), b = 15.459(2), c = 23.813(2) A?, β = 97.870(5)° and Z = 4. The carbonyl and ethylene ligands are disordered, but their positions have been adequately resolved and the structure has refined (on F²) to R1₍F₀) = 0.0344 (observed data) for 8699 unique reflections (6638 observations) and 653 parameters varied.