Ruthenium Dihydridobis(pyrazolyl)borate Complexes Adopting a κ³ N,N,H, κ² N,H, or κ² N,N Bonding Mode

Abstract

Ruthenium complexes containing the dihydridobis(3,5-bis(trifluromethyl)pyrazolyl)borate ligand Bp(CF3)2 have been prepared and structurally characterized. Reaction of (Bp(CF3)2)RuH(COD) (1a) with 2 equiv of bulky phosphines PR3 under 3 bar of H2 produces the hydrido(dihydrogen) complexes (Bp(CF3)2)RuH(H2)(PR3)2 (R = Cy, 2a; R = iPr, 3a). X-ray structural analysis of 3a confirms a κ2 N,H bonding mode of the Bp(CF3)2 ligand. In the absence of dihydrogen, the monohydride complex (Bp(CF3)2)RuH(COD)(PCy3) (4a) is isolated. Upon pressurization to 3 bar H2, 4a converts into (Bp(CF3)2)RuH(H2)(PCy3) (5a) with rechelation of the pendant pyrazolyl ring and hydrogenation of the COD ligand. Addition of 2 equiv of PPh3 or Ppyl3 to 1a under 3 bar of H2 leads to the formation of the corresponding hydrido complexes (Bp(CF3)2)RuH(PR3)2 (R = Ph, 6a; R = pyl, 7a). Under similar conditions, 1a reacts with 2 equiv of tBuNH2 to produce the amine adduct (Bp(CF3)2)RuH(tBuNH2)2 (8a). By addition of 1 equiv of MeI to 8a, the iodo complex (Bp(CF3)2)RuI(tBuNH2)2 (9a) is isolated and characterized by an X-ray structural determination. The analogous chloro complex (Bp(CF3)2)RuCl(tBuNH2)2 (10a) can be prepared by stirring a dichloromethane solution of 8a for 18 h. In the absence of dihydrogen, 1a reacts with a large excess of tBuNH2 to give (Bp(CF3)2)RuH(COD)(tBuNH2) (11a). The structure with a κ2 N,H coordination of the Bp(CF3)2 ligand is confirmed by an X-ray determination. Using the more sterically demanding diisopropylamine in the same conditions used for the formation of 8a, we could not isolate any complex. However upon N2 atmosphere, the dinuclear species with a μ2-bridging dinitrogen ligand [(Bp(CF3)2)RuH(iPr2NH)]2(N2) (12a) could be isolated and characterized by a single-crystal X-ray determination. Addition of mesitylene to 1a produces the arene complex (Bp(CF3)2)RuH(η6-C6H3Me3) (13a). The X-ray structure determination gave conclusive evidence for the κ2 N,N bonding mode of the Bp(CF3)2 ligand. When exposing 1a to a CO atmosphere, the new acyl(dicarbonyl) complex (Bp(CF3)2)Ru(COC8H13)(CO)2 (14a) is isolated in very high yield. Its structure is fully characterized on the basis of 2D homonuclear and heteronuclear correlation NMR data and by an X-ray structural determination. Similar reactions have been performed using the nonfluorinated complex (BpMe2)RuH(COD) (1b) as starting material. The analogous complexes 2b, 4b−6b, and 14b have been obtained. The variation of of the hapticity of the Bp ligand plays a crucial role in this chemistry, but the fluorinated substituents have a limited influence.