Borole Derivatives. 23. Reversible Carbonylation and Lewis Base Degradation of the Heterocubane [Rh(μ3-I)(C4H4BPh)]4and of the Bis(borole) Complex RhI(C4H4BPh)2and Synthesis and Structure of the Dinuclear Complex Cp*Rh(μ-I)3Rh(C4H4BPh)1

The heterocubane [Rh(μ 3 -I)(C 4 H 4 BPh)] 4 ( 2a ) readily adds Lewis bases to form the mononuclear products RhI(py) 2 (C 4 H 4 BPh) ( 4 ), and RhI(bpy)(C 4 H 4 BPh) ( 7 ), the labile solution species RhI(NCMe) 2 (C 4 H 4 BPh) ( 8 ) and RhI(CO) 2 (C 4 H 4 BPh) ( 9 ), RhI(PPh 3 ) 2 (C 4 H 4 BPh) ( 11 ), the 1,1‘-bis(diphenylphosphino)ferrocene complex RhI(dppf)(C 4 H 4 BPh) ( 13 ), and the norbornadiene complex RhI(nbd)(C 4 H 4 BPh) ( 14 ) as well as the dinuclear products [Rh(μ-I)(py)(C 4 H 4 BPh)] 2 ( 5 ), [Rh(μ-I)(CO)(C 4 H 4 BPh)] 2 ( 10 ), and the bis(diphenylphosphino)methane complex [Rh 2 (μ-I) 2 (μ-dppm)(C 4 H 4 BPh) 2 ] ( 12 ). The complexes 5 and 10 exist as mixtures of cis and trans isomers; the isomeric carbonyls 10 interconvert slowly at ambient temperature, while the isomeric pyridine complexes 5 show fast interchange on the NMR time scale at 20 °C and low-temperature limiting spectra at −80 °C. The heterocubane also adds (RhI 2 Cp*) 2 (which acts as a Lewis base and as a Lewis acid) to produce the novel unsymmetrical dinuclear complex Cp*Rh(μ-I) 3 Rh(C 4 H 4 BPh) ( 15 ). Complex 15 was shown by crystal structure analysis to possess a central trigonal-bipyramidal Rh 2 I 3 core, capped with the Cp* and the borole ligands, respectively. The bis(ligand) complex RhI(C 4 H 4 BPh) 2 ( 3a ) reacts with excess pyridine at 20 °C to give RhI(py) 2 (C 4 H 4 BPh) ( 4 ) and the borole-pyridine adduct C 4 H 4 BPh·py ( 6 ). With CO it reacts at elevated temperature (in toluene, 80 °C, 7 h) to give the dicarbonyl 9 with loss of one borole ligand.