Metallacyclic yttrium alkyl and hydrido complexes: synthesis, structures and catalytic activity in intermolecular olefin hydrophosphination and hydroamination

Metallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr(2)C(6)H(3)NC(Me)=C(Me)NC(6)H(3)iPr(2)-2,6] = L-1) [L-1]Y(CH2SiMe3)(THF)(2) (2), {[L-1]Y(CH2SiMe3)(2)}(-){Li-(THF)(4)}(+) (3), [L-1] Y(OEt2)(mu-Me)(2)Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L1] Y(THF) 2(mu-Cl) 2Li(THF) 2 (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H-2 or PhSiH3 afford the dimeric hydride {[L-1]Y(THF)(mu-H)}(2)(mu-THF) (5) containing two mu-bridging hydrido and one mu-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed eta(2)-coordination of the C=C fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal-ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C-O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L-1]Y}(3)(mu(2)-OMe)(3)(mu(3)-O)](2-)[Li(DME)(3)](2)(+) (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH2 and Ph2PH as well as hydroamination of styrene and pyrrolidine.