METALLACYCLES WITH STEREOGENIC METAL CENTERS - SYNTHESIS AND CHARACTERIZATION OF DIASTEREOMERIC CYCLORUTHENATED CHIRAL AMINES

The transmetalation reaction of enantiomerically pure (R)(C)- or (S)(C )-(HgCl[C6H4CH(Me)NMe(2)]} with [(eta(6)-arene)RuCl2](2) dimers, where eta(6)-arene (toluene, 2), and 1-Me-4-Pr-i-C6H4 (cymene, 3), in CH3CN at ambient temperatures forms in each case a mixture of two diastereo meric ruthenacycles [(R)(C)(S)(Ru)-a, major, and (R)(C)(R)(Ru)-a', min or, or (S)(C)(R)(Ru)-b', major, and (S)(C)(S)(Ru)-b', minor] of the ty pe ((eta(6)-arene)RuCl[C6H4CH(Me)NMe(2)]} (1a-a', 2a-a',3a-a' or 1b-b' , 2b-b', 3b'-b) in good chemical and optical yields. The diastereosele ctivity of these reactions, which molecular mechanics calculations sug gest to be under kinetic control, varies as a function of the nature o f the arene ligand (de is the diastereomeric excess): benzene(90% de) > toluene (87% de) > cymene (67% de). These complexes are characterize d in solution by a variety of spectroscopic techniques (H-1- and C-13- NMR, UV, CD) and in the solid-state by single-crystal X-ray crystallog raphy and far-IR. X-ray crystallographic studies, carried out on 1b', 2b', and 3a, establish the absolute configuration at the chiral Ru cen ter in each. Both 1b' and 2b' crystallize in the orthorhombic space gr oup P2(1)2(1)2(1), Z = 4, but 3a crystallizes in the monoclinic space group P2(1), Z = 2. Unit cell parameters for: 1b': a = 12.886(3) Angst rom, b = 17.254(5) Angstrom, c = 6.726(2) Angstrom, V = 1495.4 Angstro m(3). For 2b': a 12.523(3) Angstrom, b = 18.679(5) Angstrom, c 6.765(2 ), V = 1582.6 Angstrom(3). For 3a: a = 14.050(4) Angstrom, b = 6.633(1 ) Angstrom, c = 10.131(3), V = 942.5 Angstrom(3). The latter data show that of the two possible diastereomeric envelope conformations of the five-membered chelate ring in each compound only the one with a minim um C-CH3 ...eta(6)-arene interaction is formed. NMR (CDCl3) studies sh ow that the Ru-N bond is preserved in solution, leading to configurati onally-stable (at Ru), optically-active species. Moreover, H-1 differe nce NOE spectroscopy reveals the existence of a dynamic equilibrium be tween the two limiting conformations of the five-membered chelate ring in each diastereomeric ruthenacycle.