ARYL COMPOUNDS OF RHODIUM - SYNTHESES AND X-RAY CRYSTAL-STRUCTURES

The interactions of fac-RhCl3(tht)3, tht = tetrahydrothiophene, with aryl-lithium or -magnesium bromide reagents, aryl = 2,4,6-R3C6H2 (R = Me or Pr(i)), 2,6-Me2C6H3, or 2-MeC6H4, and also Mg(PhCH2)Br, have been studied. With Li(2,4,6-Pr(i)3C6H2)(Et2O) only the unique, square, paramagnetic rhodium(II) compound trans-Rh(2,4,6-Pr(i)3C6H2)2(tht)2 is obtained. This reacts with CO reversibly to give labile carbonyl species and with Bu(t)NC to give the rhodium(I) sigma-bonded iminoacyl Rh(CNBu(t))3(2,4,6-Pr(i)3C6H2C = NBu(t)). A similar mesityl (mes) compound is obtained from Rh(mes)3 and Bu(t)NC. Homoleptic rhodium(III) aryls Rh(aryl)3 have been obtained for aryl = 2,6-Me2C6H3 and 2,4,6-Me3C6H2. The mesityl reacts with CO to give a carbonyl species that has a bridged acyl and a bridge in which a mesityl group sigma-bonded to one Rh atom is bound eta-6 to the other. It also reacts with PMe2Ph to give Rh(mes)(PMe2Ph)3. The interaction of RhCl3(tht)3 with Mg(PhCH2)Br gives only the unsymmetric bridged species (tht)(PhCH2)2Rh(mu-Cl)3Rh(CH2Ph)(tht)2. The crystal structures of six compounds have been determined: trans-Rh(2,4,6-Pr(i)3C6H2)2(tht)2 is square with a two-fold axis of symmetry perpendicular to the molecular plane [Rh-C and Rh-S 2.11(1) and 2.291(5) angstrom]. The compounds Rh(CNBu(t))3(sigma-RC = NBu(t)), (R = 2,4,6-Me3C6H2 or 2,4,6-Pr(i)3C6H2) have similar structures in which the rhodium(I) centres are square [Rh-C (isocyanide) and Rh-C (imino) 1.88-1.94(2) and 2.08 and 2.06(2) angstrom]. The compound Rh2(2,4,6-Me3C6H2CO)(2,4,6-Me3C6H2(CO)3 contains two rhodium centres with quite different co-ordination: Rh(1) is square with bonds to two carbonyls [Rh-C 1.81(1) and 1.90(1) angstrom], an aryl [Rh-C 2.07(1) angstrom] and an oxygen from the aroyl ligand [Rh-O 2.08(1) angstrom]; Rh(2) is trigonal bipyramidal with the aryl sigma-bonded to Rh(1) now eta-6 bonded over two equatorial [Rh-C 2.33(1) and 2.34(1) angstrom] and one axial [Rh-C 2.44(1) angstrom] sites, the remaining axial and equatorial sites being occupied by the aroyl carbon [Rh-C 1.94(1) angstrom] and a carbonyl group [Rh-C 1.84(1) angstrom]. The compound Rh(2,4,6-Me3C6H2)(PMe2Ph)3 has square rhodium(I) geometry [Rh-C 2.09(1) and Rh-P 2.304(4) angstrom (trans to the aryl) and 2.276(4) and 2.287(4) angstrom trans to each other]. The dimer Rh2(PhCH2)3Cl3(tht)3 has a confacial bioctahedral structure with Rh-Cl, Rh-C and Rh-S distances showing considerable variations due to the differing trans influences of the three ligand types.