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 = Bu^t or C₆H₄Me-p) to give [(OC)IRh(µ-pz)(µ-dppm)₂Rhl(CNR)]ClO₄[R = Bu^t(3) or C₆H₄Me-p(4)]via[(OC)IRh(µ-pz)(µ-CO)(µ-dppm)₂Rhl(CNR)]ClO₄[R = Bu^t(1) or C₆H₄Me-p(2)] and, finally, [Rh₂(µ-pz)I₂(CNR)₂(µ-dppm)₂] ClO₄[R = Bu^t(7) or C₆H₄,Me-p(8)]via[Rh₂(µ-pz)I₂(µ-CO)(CNR)₂(µ-dppm)₂]ClO₄[R = Bu^t(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(CNBu^t)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)Å, 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)Å, are connected by a triple bridge, involving two dppm ligands and the pyrazolate anion.