Reactivity of binuclear pyrazolate-bridged rhodium complexes with isocyanides. Molecular structure of [Rh2(µ-pz)I2(CNBut)2–(µ-Ph2PCH2PPh2)2]BF4(pz = pyrazolate)

Abstract

The CO groups of [Rh2(µ-pz)I2(CO)2(µ-dppm)2]ClO4(pz = pyrazolate, dppm = Ph2PCH2PPh2) have been gradually substituted by reaction with isocyanides CNR (R = But or C6H4Me-p) to give [(OC)IRh(µ-pz)(µ-dppm)2Rhl(CNR)]ClO4[R = But(3) or C6H4Me-p(4)]via[(OC)IRh(µ-pz)(µ-CO)(µ-dppm)2Rhl(CNR)]ClO4[R = But(1) or C6H4Me-p(2)] and, finally, [Rh2(µ-pz)I2(CNR)2(µ-dppm)2] ClO4[R = But(7) or C6H4,Me-p(8)]via[Rh2(µ-pz)I2(µ-CO)(CNR)2(µ-dppm)2]ClO4[R = But(5) or C6H4Me-p(6)]. The CO bridging groups of (1), (2), (5), and (6) are ketonic carbonyls according to their spectroscopic properties. The reactivity of [Rh2(µ-pz) I2(CO)2(µ-dpam)2]ClO4(dpam = Ph2AsCH2AsPh2) with isocyanides was studied for comparison. The structure of the BF4–analogue of (7), [Rh2(µ-pz)I2(CNBut)2(µ-dppm)2]BF4(7b), has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21/n with unit-cell parameters a= 20.347(8), b= 21.221(8), c= 14.514(6)A, β= 94.11(2)°, and Z= 4. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by block-matrix least squares to R= 0.0630 for 4 969 observed reflections. In the cationic complex the two Rh atoms, at a distance of 2.829(3)A, are connected by a triple bridge, involving two dppm ligands and the pyrazolate anion.