METAL-LIGAND MULTIPLE BONDS IN ORGANOMETALLIC COMPLEXES CONTAINING TRIAMIDOAMINE LIGAND SYSTEMS by JOEL

Chapter 1 The synthesis and reactivity of [N3N]Ta=E complexes is presented where E is a la, l or la, 21t donor and [N3N] 3= [(Me3SiNCH 2CH2)3N]. [N3N]Ta=PPh reacts with excess lithium metal in tetrahydrofuran to give "[N3N]Ta=PLi" which reacts with RX at -35 'C to afford the phosphinidene complexes, [N3N]Ta=PR (R = Me, n-Bu, SiMe3 , SiMe2Ph). [N3N]TaCl 2 reacts with two equivalents of LiN(H)R (R = H, CMe3, Ph) to produce imido complexes, [N3N]Ta=NR, and with two equivalents of benzylmagnesium chloride or trimethylsilylmethyllithium to afford the alkylidene complexes, [N3N]Ta=CHR. The ethylene complex, [N3N]Ta(rI -C2H4), is formed quantitatively upon adding two equivalents of ethylmagnesium chloride to [N3N]TaCl2. An X-ray structure of [N3N]Ta(Me)Et, a precursor to [N3N]Ta(Tl 2 -C2H4) in a first order reaction, shows it to be a six coordinate species with two alkyl ligands in crowded apical coordination sites. [N3N]Ta(Tl -C2H4) decomposes in a first order manner to afford a complex in which a C-N bond in the tren backbone has been cleaved. Alkylation of [N3N]TaCl 2 with two equivalents of RCH2CH 2MgX (R = CH 3 , CH2 CH3, CH(CH 3)2 , C(CH 3)3; X = Cl or Br) produces a mixture of alkylidene and decomposition products. [N3N]TaCl 2 reacts with two equivalents of vinylmagnesium bromide to afford [N3N]Ta(Tj-C2H2), which has been characterized by an X-ray study. An analogous benzyne complex can be prepared by refluxing [N3N]TaCI 2 with two equivalents of phenyllithium in toluene for 1 day. [N3N]Ta(Me)Ph can be s nthesized and shown to convert into [N3N]Ta(1T-C6 H4) in a first order reaction. [N3N]Ta(1R -C2H4 ) reacts with a catalytic amount of phenylphosphine to afford [N3N]Ta=CHMe, while reactions with ammonia, aniline, or pentafluoroaniline yield [N3N]Ta=NR complexes. In contrast, addition of an excess of Me3 SiAsH2 to [N3N]Ta(Tl -C2H4) affords [N3N]Ta=CHMe immediately, and then over a period of days, what is proposed to be [N3N]Ta=AsSiMe 3 . [N3N]Ta(lT-C6H4) reacts with ArNH2 (Ar = Ph, C6F5) to give [N3N]Ta=NAr complexes and PhAsH2 to afford [N3N]Ta=AsPh. Chapter 2 The synthesis and reactivity of [N3N*]Ta=E complexes is described where E is a la, 1It or la, 2r donor and [N3N*] 3= [(Et3SiNCH 2CH 2 )3N]-. Tris(2-aminoethyl)amine (tren) reacts successively with three equivalents of n-butyllithium and three equivalents of triethylchlorosilane in tetrahydrofuran to form H3[N 3N*] quantitatively. Deprotonation of H3[N 3N*] with three equivalents of n-butyllithium generates Li3 [N3N*] in situ, which is then treated with TaCI5 to afford [N3N*]TaCl 2. [N3 N*]TaMe2 is formed quantitatively upon adding two equivalents of mnethylmagnesium chloride to [N3N*]TaCl 2 . Alkylation of [N3N*]TaCl 2 with two equivalents of ethylmagnesium chloride yields [N3N*]Ta(12-C2H4) along with -10% [N3N*]Ta=CHMe, while addition of two equivalents of alkyllithium or Grignard reagent RCH2 M (R = CH 2CH 3 , CH 2 CH 2 CH 3, CH 2 CH(CH 3 )2 , Ph, SiMe3; M = Li, MgCl or MgBr) yields the alkylidene complexes, [N3N*]Ta=CHR. [N3N*]TaMe 2 decomposes upon thermolysis to afford MeTa[N(SiEt 3)(CH=CH 2)][N(CH 2CH 2NSiEt3 )2], while [N3N*]Ta(l12-C 2H4) decomposes in a first order manner (k = 4.23 (4) x 105 s1 at 70 'C) to produce EtTa[N(SiEt 3)(CH=CH2 )][N(CH 2CH2NSiEt3)2]. An X-ray structure of the latter demonstrates it to be a distorted trigonal bipyramid in which a C-N bond in the original tren backbone has been cleaved. An equimolar mixture of [N3N*]Ta(l2-C 2H2) and { [N3N*]Ta=CHCH 2 12 is formed upon treating [N3N*]TaCl 2 with two equivalents of vinylmagnesium bromide in refluxing toluene. An X-ray structure of { [N3N*]Ta=CHCH 2 12 shows it to contain two distorted trigonal bipyramidal [N3N*]Ta units bridged by a four carbon "dialkylidene" unit in which the alkylidenes are severely "distorted" (average Z Ta=C-C = 1730 ). These results are compared and contrasted with those obtained in analogous [N(CH 2CH2NSiMe3)3] tantalum chemistry. Chapter 3 The synthesis and reactivity of [N3N]NbX complexes is presented where X is a nitrogenor oxygen-based donor and [N3N] 3= [(Me 3SiNCH 2 CH 2 )3N] 3-. The reactions of NbCl5 , NbCl 4 (THF)2 , and NbCl 3(dme) with Li3 [N3N] in a variety of solvents do not produce an identifiable [N3N]NbCln (n = 0, 1, 2) species. NbOCl 3 (THF)2 and Nb(NSiMe 3)C13 (py)2 react with one equivalent of Li 3 [N 3N]*THF 2 to afford [N3N]Nb=O and [N3N]Nb=NSiMe 3 , respectively, in good yields. [N3N]Nb=O reacts with triethylaluminum to form the base adduct [N3N]Nb=O*A1Et 3 as judged by 1H, 13C, and 27A1 NMR. The oxo species reacts quantitatively with Me 3 SiX (X = OTf, I) to prepare [N3 N]NbOSiMe 3 +X and MeOTf to afford [N3N]NbOMe+OTf -. These du salts are reduced in high yield by sodium amalgam to provide d1 [N 3N]NbOR (R = SiMe 3 , Me). The reaction of [N3 N]NbOSiMe 3 with SiCl 4 provides [N3N]NbOSiCl 3 in moderate yield. Thesis Supervisor: Dr. Richard R. Schrock Title: Frederick G. Keyes Professor of Chemistry