Polyhedron Vol. 6, No. 6, pp. 1427-1431, 1987 Printed in Great Britain 0277~5387187 $3.W+.@l 0 1987 PCQWUOO Journals Ltd RHODIUM(I) COMPLEXES WITH THE 2,2’-BIPYRIMIDINE LIGAND MARIA P. GARCIA, JOSE L. MILLAN, MIGUEL A. ESTERUELAS and LUIS A. ORO* Departamento de Quimica InorgAnica, Instituto de Ciencia de Materiales de Aragbn, Universidad de Zaragoza-Consejo Superior de Investigaciones Cientificas, 50009 Zaragoza, Spain zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR (Received 5 December 1986 ; accepted 22 January 1987) Abstract-Mono- and dinuclear rhodium(I) complexes of formulae [Rh(L,)(bipym)]+ and [(Rh(L2)}2@-bipym)]2f [L2 = diolefin or (CO),] have been prepared and their cata- lytic activity in hydrogen-transfer reactions explored. The heterodinuclear [Cl,Pd(p- bipym)Rh(tfb)]ClO, complex was obtained by reacting [Rh(tfb)(bipym)]+ with [PdCl,(cod)] or alternatively from [Rh(tfb)(acetone),]+ with [PdCl,(bipym)]. Ion-pair complexes of for- mulae [Rh(diolefin)(bipym)]+[RhCl,(diolefin)]- (diolefin = cod, nbd or tfb) were prepared by adding bipym to acetone suspensions of [RhCl(diolefin)],. The preparation and properties of cationic rho- dium(1) complexes with chelating nitrogen donor ligands are of growing interest;lm3 in particular, some of them, containing diolefins as ancillary ligands, are active catalyst precursors for hydrogen- transfer reactions.“7 There is also an increasing interest in the synthesis of mixed-valence or homo- and heterobinuclear complexes with bidentate bridging ligands,8 due to the possibility of exploring their electronic interactions in a fundamental way and also utilizing such complexes for multi- electron transfer catalysis ; very recently a cationic ruthenium(II)-palladium(I1) binuclear complex, and binuclear platinum(I1) complexes bridged by 2,2’-bipyrimidine (bipym) have been reported.’ In this paper we describe some neutral and cationic rhodium(l) complexes, as well as a rhodium(Ik palladium(I1) complex, with the bipym ligand which can potentially act as a chelate or “bidentate” bridging ligand between two metal centers. RESULTS AND DISCUSSION A general route for the synthesis of cationic spe- cies of the type [Rh(L,)(bipym)]+ F2 = tetra- fluorobenzobicyclo(2,2,2)octatriene (tfb), bicyclo- (2,2,l)heptadiene (nbd), 1,5-cyclooctadiene (cod) *Author to whom correspondence should be addressed. or (CO) 2](compounds zyxwvutsrqponmlkjihgfedcbaZYXW l-4) involves the reaction of the solvated [Rh(L,)(Me,CO)JClO, intermediate with bipym, in the stoichiometric ratio 1: 1. Com- pound 4 was also obtained by bubbling carbon monoxide through a dichloromethane solution of any of the [Rh(diolefin)(bipym)]C104 complexes, or by reaction of [Rh(acac)(CO)2] (acac = acetylacetonate) with bipym in the presence of per- chloric acid. After working up the compounds were isolated as air-stable microcrystalline solids in good yield ; they are 1 : 1 electrolytes in acetone or nitromethane, and their IR spectra show bands due to the uncoordinated perchlorate anion at cu 1100s and 620s cm-‘. Complex 4 shows, in dichloro- methane solution, two strong v(C0) bands at 2105 and 2050 cm- ’ typical of cis-dicarbonyl derivatives, lo suggesting an electron density on the rhodium atom similar to that found for related 2,2’- bipyridine or 1, lo-phenanthroline cationic com- plexes. ‘o,1’ The coordinated bipym ligand in these complexes has two prominent bands near 1570 and 1550 cm-’ assigned to ring-stretching modes, a strong band at cu 745-750 cm-‘, due to the C-H bending mode, and one near 660 ascribed to the ring-bending mode of the phenyl groups. The low solubility of these compounds, in most solvents, prevented the obtaining of NMR spectra. Most probably, the mononuclear [Rh(L,) (bipym)]+ complexes are square-planar with the bipym ligand acting in a bidentate way. Thus, these 1427