A series of guanidine proligands, 2-(4-(tertbutyl)
phenyl)-1,3-diisopropylguanidine (1), 2-(4-bromophenyl)-
1,3-diisopropylguanidine (2), 2-(4-methoxyphenyl)-1,3-
diisopropylguanidine (3), and 2,2′-(1,4-phenylene)bis(2′,3-
diisopropylguanidine) (4), has been reacted with
[NbBz3(NtBu)] (5) through a protonolysis reaction to obtain
new monoguanidinate-supported dibenzyl niobium complexes,
{NbBz2(NtBu)[(4-tBuC6H4)NC(NiPr)(NHiPr)]} (6), {NbBz2(NtBu)[(4-BrC6H4)NC(NiPr)(NHiPr)]} (7),
{NbBz2(NtBu)[(4-MeOC6H4)NC(NiPr)(NHiPr)]} (8), and the dinuclear complex {[NbBz2(NtBu)]2[(C6H4)(NC(NiPr)-
(NHiPr))2]} (9). Complexes 6, 8, and 9 were structurally characterized. These neutral complexes contain a η2-benzyl ligand
coordinated to the metal center. Insertion migratory reactions with isocyanides resulted in the formation of bis-κ2-iminoacyl
species, {Nb(NtBu)(tBuNCCH2Ph)2[(4-tBuC6H4)NC(NiPr)(NHiPr)]} (10), {NbBz2(NtBu) (tBuNCCH2Ph)2[(4-
BrC6H4)NC(NiPr)(NHiPr)]} (11), {Nb(NtBu)(tBuNCCH2Ph)2[(4-MeOC6H4)NC(NiPr)(NHiPr)]} (12), and the
dinuclear complex {[Nb(NtBu)(tBuNCCH2Ph)2]2[(C6H4)(NC(NiPr)(NHiPr))2]} (13), when tBuNC was used. The
analogous reaction using XyNC (Xy = 2,6-Me2C6H3) led to the formation of vinylamido species, {Nb(NtBu)[N(2,6-
Me2C6H3)CHCHPh][BzCN(2,6-Me2C6H3)][(4-tBuC6H4)NC(NiPr)(NHiPr)]} (14), {Nb(NtBu)[N(2,6-Me2C6H3)-
CHCHPh][BzCN(2,6-Me2C6H3)][(4-BrC6H4)NC(NiPr)(NHiPr)]} (15), {Nb(NtBu)[N(2,6-Me2C6H3)CHCHPh]-
[BzCN(2,6-Me2C6H3)][(4-MeOC6H4)NC(NiPr)(NHiPr)]} (16), and {[Nb(NtBu)[N(2,6-Me2C6H3)CHCHPh]-
[BzCN(2,6-Me2C6H3)]]2[(C6H4)[NC(NiPr)(NHiPr)]2]} (17), through a proposed 1,2-hydrogen shift mechanism from
an iminoacyl intermediate similar to those obtained from the insertion of tBuNC. Complex 17 was structurally characterized
