The structure and chemistry of tris(pentafluorophenyl)borane protected mononuclear nitridotitanium complexes

Abstract

Treatment of TiCl(NMe(2))(3) with H(3)N·B(C(6)F(5))(3) results in N-H activation and ligand exchange to yield the structurally characterised salt [TiCl(NMe(2))(2)(NMe(2)H)(2)](+)[Ti[triple bond]NB(C(6)F(5))(3)(Cl)(2)(NMe(2)H)(2)](-). Cation exchange with [Me(4)N]Cl, [Ph(4)P]Cl and [(PhCH(2))Ph(3)P]Cl yields the respective ammonium and phosphonium salts of the [Ti[triple bond]NB(C(6)F(5))(3)(Cl)(2)(NMe(2)H)(2)](-) anion. X-ray crystallography reveals that the essential trigonal bipyramidal geometry and composition of the anion is retained in each of these salts despite some minor variations in the Ti-N-B angle and the nature of the interionic interactions. Electronic investigation by DFT calculations confirmed the Ti-N triple bond character implied by the experimentally determined bond length, with the HOMO and HOMO-1 having Ti-N π-bonding character. The dimethylamine ligands of the anion resist substitution by moderate bases but can be displaced by pyridine to give a pentacoordinate anion. In contrast, addition of 2,2'-bipyridyl gives a neutral octahedral complex. Treatment of the pyridine complex with TlCp results in the formation of a four coordinate anionic cyclopentadienyl complex.

Synthesis and Structure of Amido‐ and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: NH and BH Activation

“…[30] The ZrÀN bond lengths in 5·PhMe reflect this difference in bonding pattern, with the shorter 2.263 (8) bond of the agostic ligand being essentially identical in length to that in VIa, while the and Zr À N2 bond length is 2.335 (8) . A shorter N1 À B1 bond at 1.520(13) is observed for the agostically bonded ligand in comparison to both the non-agostic ligand, where N2ÀB2 is 1.602 (13) , and the free borane (1), in which the corresponding bond length is 1.6034 (19) . The structural chemistry of the b-Bagostic amidoboranes mirrors that of b-agostic alkyls: the Ca À Cb bond length in [(MeCp) 2 Zr(Et)A C H T U N G T R E N N U N G (PMe 3 )] + is 1.47(2) versus 1.532(2) for the C À C bond in ethane.…”

“…The [NHBA C H T U N G T R E N N U N G (C 6 F 5 ) 2 H] 2À ligand can be formally regarded as a Lewis acid stabilised terminal imido or imidoborane ligand, thus complementing the amidoborane and nitridoborane examples we have recently reported. [16][17][18][19][20][21] The coordination sphere of 9·PhMe is all the more remarkable, because imido zirconocene and hafnocene complexes have previously required stabilisation with bulky nitrogen substituents. Even then, such compounds could only be isolated with basic donor ligands occupying the coordination site taken by an agostic interaction in 9·PhMe.…”

“…In earlier work, we demonstrated the synthesis of amidoborane and ultimately nitridoborane complexes through sequential N À H activation of the adduct H 3 N·BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 following the reaction with metal bases (Scheme 2). [16][17][18][19][20][21] Metallocene complexes of the [NH 2 BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 ] À ligand were prepared through treatment of the electrophilic zwitterions [Cp 2 MMe- 3 ]. [16] This work has played an important role in illustrating N À H activation pathways, but BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 derived ligands are of limited value as models for intermediates in the catalytic reactions, because of the absence of b-hydrides.…”

Molecular titanium nitrides: nucleophiles unleashed

“…1). 42–44 However, examples of well-defined group 4 nitrides are indeed known, and can be isolated as dinuclear (Fig. 1), trinuclear (Fig.…”

“…1), tetranuclear, and even hexanuclear species. 42–51 Thus, we focused our attention on group 4, especially on Ti, since reactivity studies of mononuclear nitrides in this group have largely evaded the reach of the synthetic chemist until recently. 52,53 The fact that mononuclear titanium nitrides are exceedingly rare is rather surprising since group 4 nitrides have been proposed in N 2 activation and reductive splitting reactions, and the nitride group is often generated in route to the deposition of thin metal nitride films.…”