[o-phenylenebis(dimethylarsine)]heptacarbonyldiiron. Preparation, crystal structure, and fluxionality in solution

Article abstract of DOI:10.1021/ic00131a054

The reaction of Fe₂(CO)₉ with o-phenylenebis(dimethylarsine), diars, in an atmosphere of CO gives yellow (diars)Fe₂(CO)₈ and red (diars)Fe₂(CO)₇, separable by chromatography on silica. The red compound crystallizes in space group P1 with Z = 2 and the following unit cell dimensions: a = 9.706 (4) ?; b = 11.876 (3) ?; c = 9.576 (3) ?; α = 92.41 (2)°; β = 104.81 (2)°; γ = 91.25 (2)°; V= 1066 (1) ?³. The structure consists of dinuclear molecules in which diars is chelated on one iron atom (Fe(1)) to which are also bound two terminal CO groups. Fe(1) also forms a metal-metal bond, 2.566 (1) ?, to Fe(2), which bears three strictly terminal CO groups. Of the remaining two CO groups, one forms a nearly symmetrical bridge while the other is semibridging with its short bond, 1.894 (7) ?, to Fe(2) and its long bond, 2.103 (7) ?, to Fe(1). The ¹³C NMR spectrum is highly temperature dependent, changing from a five-line spectrum (1:2:2:1:1) at -132°C to a single-line spectrum at 11°C. A three-stage process for equivalencing all of the CO's is proposed.