Synthesis, Structures, and DFT Bonding Analysis of New Titanium Hydrazido(2−) Complexes

Abstract

The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2-) species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric mu-eta2,eta1-bridged compounds Ti2(mu-eta2,eta1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3 showed the formation of N-H...Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(N(t)Bu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti2(mu-eta2,eta1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2-) chemistry of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2[HC(Me2pz)3] (9, structurally characterized), and Ti(NNPh2)Cl2[HC(n)Bupz)3] (10) in good yields (Me3[9]aneN3 = trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 = trimethyl-1,3,5-triazacyclohexane, HC(Me2pz)3 = tris(3,5-dimethylpyrazolyl)methane, and HC((n)Bupz)3 = tris(4-(n)butylpyrazolyl)methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2[HC(pz)3] (I) and the corresponding imido compounds Ti(NMe)Cl2[HC(pz)3] (II) and Ti(NPh)Cl2[HC(pz)3] (III). The NNPh2 ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metalligand triple bond), but with one of the Ti=N(alpha) pi components significantly destabilized by a pi interaction with the lone pair of the N(beta) atom. The NR ligand sigma donor ability was found to be NMe > NPh > NNPh2, whereas the overall (sigma + pi) donor ability is NMe > NNPh2 > NPh, as judged by fragment orbital populations, Ti-N atom-atom overlap populations, and fragment-charge analysis. DFT calculations on the hydrazido ligand in a mu-eta2,eta1-bridging mode showed involvement of the N=N pi electrons in donation to one of the Ti centers. This TiN2 interaction is best represented as a metallocycle.

Early Transition‐Metal Hydrazido Complexes: Masked Metallanitrenes from NN Bond Scission

“…[7] Mountford and co-workers have reported DFT calculations suggesting that the -N b R 2 group on the a-nitrogen destabilizes the Ti=N a linkage by an N a -N b p* antibonding contribution from the N À N bond of the hydrazido to the HOMO. [10] If a change in hapticity at the hydrazido motif from h 1 to h 2 promotes metallanitrene formation, then the addition of Lewis bases should slow down the rate for these transformations. It is unlikely that a naked or terminal metallanitrene is generated in this set of reactions as the substrate must first interact with the anitrogen before irreversible N À N bond rupture ensues.…”

A Zirconium Hydrazide as a Synthon for a Metallanitrene Equivalent: Atom‐by‐Atom Assembly of [EN2]2− Units (E=S, Se) by Chalcogen‐Atom Transfer in the Coordination Sphere of a Transition Metal

“…[2,3] On the other hand, hydrazidotitanium complexes appear to be key intermediates in stoichiometric and catalytic hydrazinations of alkynes [4] and in related reactions, [5] which has recently directed attention to the Group 4 elements. [6] For the heavier Group 4 metals, only one example, [Cp 2 Zr(N 2 Ph 2 )(dmap)] (Cp = C 5 H 5 , dmap = 4-dimethylaminopyridine), has been reported, by Bergman and co-workers. In a preliminary study into the reactivity of the compound, a tendency for NÀN bond cleavage in reactions with alkynes and CO was observed.…”

Ruthenium complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane for atom and group transfer reactions

“…a acac, pentane-2,4-dionate; biqn, 1,1 -biisoquinoline; bpy, 2,2 -bipyridine; cbpy*, (−)-3,3 -[(4S-trans)-1,3-dioxolane-4,5-dimethyl]-2,2 -bipyridine; diopy*, (R,R )-3,3 -(1,2-dimethylethylenedioxy)-2,2 -bipyridine; 3,3 -Me2bpy, 3,3 -dimethyl-2,2 -bipyridine; phen, 1,10-phenanthroline. b [20,40,41], -carbene/-vinylidene/-allenylidene [42,43], -nitrido [18,44], and -carbyne [19] complexes, is depicted in Table 1.…”