ALKENE ROTATION IN [RU(ETA(5)-C5H5)(L(2))(ETA(2)-ALKENE)][CF3SO3] WITH L(2)=IPR- OR PTOL-DIAZABUTADIENE - X-RAY CRYSTAL-STRUCTURE OF [RU(ETA(5)-C5H5) (PTOL-DAB)(ETA(2)-ETHENE)][CF3SO3]

Reaction of RuCl(pi(5)-C5H5) (pToI-DAB) With AgOTf (OTf= CF3SO3) in CH 2Cl2 or THF and subsequent addition of L' (L' = ethene (a), dimethyl f umarate (b), fumaronitrile (c) or CO (d)) led to the ionic complexes [ Ru(pi(5)-C5H5) (pToI-DAB) (L')] [OTf] (2a, 2b and 2d) and [Ru(eta 5-C5 H5) (pTol-DAB) (fumaronitrile-N)] [OTf] (5c). With the use of resonanc e Raman spectroscopy, the intense absorption bands of the complexes ha ve been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(pi(5)-C5H5) (pTol-DAB) (pi(2)-ethene)] [CF3SO3] (2a) has been carried out. Crystal data for 2a: monoclinic, s pace group P2(1)/n with a = 10.840(1), b = 16.639(1), c = 14.463(2) An gstrom, beta = 109.6(1)degrees, V = 2465.6(5) Angstrom(3), Z=4. Comple x 2a has a piano stool structure, with the Cp ring pi(5)-bonded, the p Tol-DAB ligand sigma N, sigma N' bonded (Ru-N distances 2.052(4) and 2 .055(4) Angstrom), sind the ethene pi(2)-bonded to the ruthenium cente r (Ru-C distances 2.217(9) and 2.206(8) Angstrom). The C=C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angl e between the plane of the Cp ring and the double bond of the ethene i s 1.8(0.2)degrees. The reaction of RuCl(pi(5)-C5H5) (PPh(3))(2) with A gOTf and ligands L' = a and d led to [Ru(pi(5)-C5H5) (PPh(3))(2)(L')] [OTf] (3a) and (3d), respectively. By variable temperature NMR spectro scopy the rotational barrier of ethene (a), dimethyl fumarate (b) and fumaronitrile (c) in complexes [Ru(pi(5)-C5H5) (L(2)) (pi(2)-alkene)] [OTf] with L(2) = iPr-DAB (1a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh( 3) (3a) was determined. For 1a, 1b and 2b the barrier is 41.5 +/- 0.5, 62 +/- 1 and 59 +/- 1 kJ mol(-1), respectively. The intermediate exch ange could not be reached for 1c, and the Delta G(not equal) was estim ated to be at least 61 kJ mol(-1). For 2a and 3a the slow exchange cou ld not be reached. The rotational barrier for 2a was estimated to be 4 0 kJ mol(-1). The rotational barrier for methyl propiolate (HC=CC(O)OC H3) (k) in complex [Ru(pi(5)-C5H5) (iPr-DAB) (pi(2)-HC=CC(O)OCH3)][OTf ] (1k) is 45.3 +/- 0.2 kT mol(-1). The collected data show that the ba rrier of rotation of the alkene in complexes la, 2a, Ib, 2b and Ic doe s not correlate with the strength of the metal-alkene interaction in t he ground state.