1H-Pyrrolo[2,3-b]pyridine (HL) ligands in rhodium(I) and iridium(I) chemistry. Crystal and molecular structures of [Rh2(µ-L)2(nbd)2] and [Rh4(µ-Cl)2(µ-L)2(µ-CO)2(CO)2(nbd)2

Abstract

Reactions of 1H-pyrrolo[2,3-b]pyridine (HL) with [Rh(diolefin)2][ClO4] or [Rh2Cl2(diolefin)2] compounds give mononuclear [Rh(diolefin)(HL)2][ClO4] or [RhCl(diolefin)(HL)] complexes respectively. The latter react with KOH to form binuclear [Rh2(µ-L)2(diolefin)2] complexes. Carbonylation reactions of the above compounds afford [Rh(CO)2(HL)2][ClO4], [RhCl(CO)2(HL)], or [Rh2(µ-L)2(CO)4]. Some related iridium(I) complexes are also reported. Redistribution reactions take place between [Rh2(µ-L)2(diolefin)2] and [Rh2(µ-L)2(CO)4] yielding [(diolefin)Rh(µ-L)2Rh(CO)2] complexes. The tetranuclear complex [Rh4(µ-Cl)2(µ-L)2(µ-CO)2(CO)2(nbd)2] has been isolated by several routes starting from the above mono- or bi-nuclear neutral rhodium complexes. The structures of the complexes [Rh2(µ-L)2(nbd)2] and [Rh4(µ-Cl)2(µ-L)2(µ-CO)2(CO)2(nbd)2](nbd = norborna-2,5-diene) have been determined by X-ray methods. The former crystallizes in the monoclinic space group C2/c with a= 16.272(4), b= 7.932(2), c= 19.198(5)A, β= 112.07(2)°, and Z= 4. Crystals of the latter are monoclinic, space group P21/n with Z= 2 and a unit cell of dimensions a= 11.091(3), b= 16.615(6), c= 8.531(4)A, and β= 91.63(3)°. Both structures were solved by Patterson and Fourier methods and refined by full-matrix least squares to R values of 0.072 and 0.041 respectively. The structure of the binuclear complex consists of two Rh atoms bridged by two anions L co-ordinated through the two N atoms. Each Rh atom interacts also with the olefinic bonds of a nbd molecule. The ligand L is disordered and distributed in two positions. The structure of the tetranuclear complex consists of two binuclear units joined together through a double chlorine bridge, forming a planar Rh4Cl2 ring. In each binuclear unit a bidentate anion L and a carbonyl group bridge the two Rh atoms, which are directly bonded [Rh–Rh 2.686(2)A].