Structural characterization of a rearranged trinuclear iron complex with a bridging ferracyclobutene ligand

Abstract

The title compound (VII) crystallizes in the monoclinic space group P21/c, with a= 12.325(4), b= 21.075(4), c= 19.701(9)A, β= 133.54(1)°, and Z= 4. The structure was solved by direct methods from 2 921 observed reflexions measured on a diffractometer, and refined by block-diagonal least-squares techniques to R 0.053. The analysis has shown that the conversion of another trinuclear complex [Fe3(CO)8{Ph2PC4(CF3)2}(PPh2)](III) into (VII) involves CO elimination, metal–metal bond formation, and structural changes in the diphenylphosphide bridge. The principal structural features of (VII) are the presence of a dimerized phosphinoacetylene in the form of a trans-butadiene [mean C–C 1.49(1), CC 1.39(1)A] co-ordinated simultaneously to three iron atoms [mean Fe–C (π- bonded) 2.14(8) and (σ-bonded) 2.02(3)A], a bridging diphenylphosphide group [Fe–P 2.170(6), 2.288(3)A] formed by cleavage of a P–C(sp) bond of one phosphinoacetylene, and two iron–iron bonds [2.662(7)(PPh2-bridged) and 2.531(10)A]. The Ph2PC4(CF3)2 ligand remains bonded to iron via an Fe–P bond [2.238(3)A]; mean Fe–C(carbonyl)1.79(3) and C–O 1.14(2)A.