Pyrazolate A-frame rhodium complexes. Crystal structures of [Rh2(µ-dmpz)(CO)2(µ-dppm)2][ClO4] and [Rh2(µ-dmpz)I2(CO)2(µ-dppm)2][ClO4]

Abstract

New complexes of formula [Rh₂(µ-L)(CO)₂(µ-dppm)₂]⁺, having the A-frame type structure with different pyrazolate-type groups L as bridgehead ligand, have been prepared from trans-[Rh₂Cl₂(CO)₂(µ-dppm)₂](dppm = Ph₂PCH₂PPh₂). Iodine undergoes transannular oxidative addition to [Rh₂(µ-L)(CO)₂(µ-dppm)₂][ClO₄] to produce rhodium(II) complexes [Rh₂(µ-L)I₂(CO)₂-(µ-dppm)₂][ClO₄] with direct rhodium–rhodium bonds. The crystal structures of the complexes [Rh₂(µ-dmpz)(CO)₂(µ-dppm)₂][ClO₄] and [Rh₂(µ-dmpz)I₂(CO)₂(µ-dppm)₂][ClO₄](dmpz = 3,5-dimethylpyrazolate) have been determined by X-ray methods. The former crystallises in the monoclinic space group P2₁/a with unit-cell dimensions a= 22.560(9), b= 26.649(9), c= 10.221(7)Å, β= 102.68(3)°, and Z= 4. The structure has been refined to R= 0.072 on the basis of 4 342 observed reflections. The latter crystallises in the monoclinic space group P2/n with a= 16.855(6), b= 14.713(3), c= 14.008(4)Å, β= 90.66(2)°, and Z= 2. The structure has been refined to R= 0.078 (3 048 observed reflections). In both complexes two rhodium atoms are triply bridged by two molecules of dppm and by a dmpz ligand through its nitrogen atoms. In the first complex each Rh atom has a square-planar co-ordination, in the second the oxidative addition of iodine results in a change in co-ordination to octahedral and formation of a metal–metal bond [Rh–Rh 2.725(2) A].