Structural aspects and solution dynamics of the auraferraboranes [Fe4(CO)12Au2L2BH]: The crystal structures of [Fe4(CO)12Au2{P(p-MeC6H 4)3}2BH]·CH2Cl2 and [HFe4(CO)12Au2{PEt3}2B]

Article abstract of DOI:10.1021/om00113a022

Six new auraferraboranes of the general formula [Fe₄(CO)₁₂Au₂LL′BH] (L = L′ = P(c-C₆H₁₁)₃, P(p-MeC₆H₄)₃, PMePh₂, PMe₂Ph, PMe₃; L = PMePh₂, L′ = PMe₂Ph) have been prepared. Two structural types are represented, one in which the endo-hydrogen atom bridges an Fe-B edge (structure I) and one in which it bridges an Fe-Fe edge (structure II). The change in hydrogen atom location is accompanied by a rearrangement of the gold(I) phosphine moieties and a reorientation of one iron tricarbonyl unit, while essentially retaining a constant Fe₄B framework. The crystal structures of two compounds, [Fe₄-(CO)₁₂Au₂{P(p-C₆H ₄)₃)₂BH]·CH₂Cl₂ (1) and [HFe₄(CO)₁₂Au₂{PEt₃}₂B] (2), are reported, the former being representative of structure I and the latter of structure II. 1: monoclinic, P2₁/n; a = 20.891 (6), b = 13.367 (4), c = 23.441 (7) A?; β= 110.82 (3)°; V = 6118 (4) A?³; Z = 4; R(F) = 6.39%. 2: monoclinic, I2/a; a = 17.783 (5), b = 11.277 (3), c = 18.084 (7) A?; β = 106.26 (3)°; V = 3481.3 (17) A?³; Z = 4; R(F) = 4.75%. The structure of 1 is similar to that of the related cluster [Fe₄(CO)₁₂Au₂{PPh₃}₂BH] (3). In solution, a lig-and-dependent equilibrium exists between structures I and II for the clusters [Fe₄(CO)₁₂Au₂LL′BH]. The factors that control the dominance of structure I or II for a particular phosphine ligand have been investigated, and the interplay of steric and electronic effects has been assessed. Electronic factors appear to drive the gold(I) phosphine groups to interact with Fe-B rather than Fe-Fe edges of the cluster, while steric factors dictate the actual Fe₄Au₂B core geometry.