Synthesis and Reactivity of Bis(alkoxysilylamido)yttrium η2-Pyridyl and η2-α-Picolyl Compounds

The synthesis and reactivity of bis(alkoxysilylamido)yttrium pyridyl and α-picolyl complexes [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 YR (R = η 2 -( C, N )-2-NC 5 H 4 ( 1 ); R = η 2 -( C, N )-CH 2 -2-NC 5 H 4 ( 2 ); R = η 2 -( C, N )-C(H)Me-2-NC 5 H 4 ( 3 ); R = η 2 -( C, N )-C(H)Me-2-NC 5 H 3 -6-Me ( 4) ) is reported. 1 − 4 have been prepared by C−H activation of pyridine and the corresponding methyl (ethyl) and dimethyl-substituted pyridines from [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 YCH(SiMe 3 ) 2 and by salt metathesis with the appropriate lithium salts from [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 YCl·THF. The molecular structure of 2 shows that the picolyl group is bonded to yttrium in an η 3 -aza−allylic fashion. With dihydrogen, stepwise hydrogenation of the pyridyl fragment of 1 has been observed, finally yielding the 2,3-dihydropyridyl complex [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 Y−NC 5 H 8 ( 7 ). Compound 1 inserts ethene to form the α-methylpicolyl derivative 4 . Polymerization of ethene was not observed. The pyridyl compound 1 reacts with PhC⋮CH to yield the corresponding acetylide pyridine complex [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 YC⋮CPh·Py ( 8 ). The complexed pyridine can be substituted by THF to give [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 YC⋮CPh·THF ( 9 ), which easily loses THF and forms the base-free acetylide [Me 2 Si(NCMe 3 )(OCMe 3 )] 2 YC⋮CPh ( 10 ). Compounds 1 and 2 readily insert nitriles yielding imido−pyridine complexes. The imido−pyridine complexes that contain α-hydrogen readily undergo a 1,3-H shift affording the corresponding enamido−pyridine compounds. With CO, the pyridyl compound 1 gives a dipyridylketone complex {[Me 2 Si(NCMe 3 )(OCMe 3 )] 2 Y}{μ,η 2,η 2 -( N, N ‘,O)-OC(2-NC 5 H 4 ) 2 } ( 15 ).