Early transitional metal alkyl, alkylidene, and alkylidyne chemistry

Abstract

CHAPTER 1. Zirconium and hafnium complexes of several new unsymmetric diamide ligands have been prepared and their proficiency in olefin polymerization reactions evaluated. The first set of supporting ligands examined are diamido-donor ligands that contain ethylene/o-phenylene "arms" and a phenyl-substituted amine donor in the central position. These ligands are derived from the triamines, [MesitylNH-o-C6H4N(Ph)CH2CH2NHMesityl] (H2[MesNNPhMes]) and [t- Bud6-NH-o-C6H4N(Ph)CH2CH2NHMesityl] (H2[t-BuNNPhNMes]). The Zr and Hf complexes that can be isolated include [MesNNPhNMes]MX2 (M = Zr or Hf, X = NMe2, Cl, or Me) and [t- BuNNPhNMes]MX2 (M = Zr or Hf, X = NMe2, Cl, Me). The structures of [MesNNPhNMes]ZrMe2, [t-BuNNPhNMes]ZrMe2, and a dimeric species with the formula [MesitylN-o-C6H4NCH2CH2NMesityl]Zr2(NMe2)5 are reported. Abstraction of a methyl group in [MesNNPhNMes]MMe2 (M = Zr or Hf) with [Ph3C][B(C6F5)4] gives rise to cationic complexes which are active initiators for the polymerization of 1-hexene. Similar activation of [t- BuNNPhNMes]MMe2 (M = Zr or Hf) gives rise to dimeric monocations that eventually break-up and react further to yield cationic monomethyl species. In all cases the poly[1-hexene] produced in the presence of the monometallic cations was found to be atactic.

(cont.) The second ligand explored is a diamido-didonor ligand based on the diamine, rac-H2[MepyN] (rac-N,N'-di-(6- methylpyridin-2-yl)-2,2'-diaminobinaphthalene), which can be prepared through reductive amination of rac-2,2'-diaminobinaphthalene with 6-methylpyridinecarboxaldehyde. The deprotonated amine [MepyN]2- supports of variety of zirconium and hafnium complexes including [MepyN]MX2 (M = Zr, X = NMe2, Cl, OSO2CF3, CH2CHMe2, CH2Ph; M = Hf, X = NMe2, OSO2CF3, i-Bu). The solid state structures of [MepyN]Zr(CH2Ph)2, [MepyN]Zr(NMe2)Cl, [MepyN]Hf(CH2CHMe2)2, and [MepyN]Hf(OSO2CF3)2 are reported. Activation of [MepyN]Zr(CH2Ph)2 and [MepyN]Hf(i-Bu)2 with various Lewis acids leads to observable cationic alkyls that are not active towards 1-hexene polymerization. The third ligand examined is a diamide ligand based on the diamine rac-H2[HIPTN2] (HIPTN2 = (Nhexaisopropyl- 3,5-terphenyl)diaminobinaphthalene), which can be prepared through palladiumcatalyzed N-aryl coupling of diaminobinaphthalene and 3,5-bis-(2,4,6- triisopropylphenyl)bromobenzene. The reaction between H2[HIPTN2] and M(NMe2)4 (M = Ti, Zr, and Hf) yields [HIPTN2]M(NMe2)2 complexes. Other complexes of [HIPTN2]2- that can be prepared include [HIPTN2]ZrCl2, [HIPTN2]ZrMe2, [HIPTN2]Zr(CH2-t-Bu)2, [HIPTN2]HfCl2, [HIPTN2]HfMe2, and [HIPTN2]Hf(CH2CHMe2)2.

(cont.) Activation of [HIPTN2]ZrMe2 with a variety of Lewis acids gives rise to different species depending on the nature of the activator employed. For example, [HIPTN2]ZrMe2 reacts with [Ph3C][B(C6F5)4] to give a cationic complex that is active toward oligomerization of 1-hexene, while activation with B(C6F5)3 leads to formation of [HIPTN2]Zr(C6F5)2. No polymerization of 1-hexene by activated complexes of the [HIPTN2]2- ligand is observed. CHAPTER 2. Imido alkylidene initiators for the controlled polymerization of diethyl dipropargylmalonate (DEDPM) have been prepared. A vinyl alkylidene complex, 2a, containing a five-membered ring as part of a trienylidene unit can be obtained by treating Mo(NAr)(CHCMe2R)(O-t-BuF6)2 (Ar = 2,6-diisopropylphenyl; R = Me, Ph; t-BuF6 = C(CF3)2Me) with diethyl 3-(2-methylprop-1- enyl)-4-vinylcyclopent-3-ene-1,1-dicarboxylate in pentane. A related complex, 4b, containing a six-membered ring alkylidene ligand can be prepared by a reaction between Mo(NAr)(CH-t- Bu)(O-t-BuF6)2 and 1-methylidene-5,5-bis(carboxyethyl)cyclohex-1-ene. Treatment of 2a or 4b with LiO-t-Bu yields the analogous tert-butoxide species (2c and 4c). An X-ray structure of a sample of 4c that retained two equivalents of LiO-t-BuF6 shows it to be a dimeric species in which two Mo complexes were joined through a Li4O4 heterocubane-type structure binding to one ester in each complex.

(cont.) Reactions between DEDPM and 4c demonstrate smooth initiation with a kp/ki value of less than one. The carboxylate species, Mo(NR)(CHCMe2R')(O2CCPh3)2 (R = various aryl groups or 1-adamantyl; R' = Ph or Me) can be prepared by salt metathesis reactions between Mo(NR)(CHCMe2R')(OTf)2(DME) (OTf = trifluoromethanesulfonate; DME = 1,2-dimethoxyethane) and sodium triphenylacetate. Trimethylphosphine adducts of selected triphenylacetate complexes can also be synthesized, and the X-ray structure of Mo(NAr'')(CH-t- Bu)(O2CCPh3)2(PMe3) (Ar'' = 2-tert-butylphenyl) is reported. Several of the triphenylacetate complexes are active initiators for the regioselective polymerization of DEPDM. Several of the alkylidene initiators serve as precursors to oligomeric fragments of poly[DEDPM], which represent structural models of the polymer chain. CHAPTER 3. Reaction of Mo(NR)(CHCMe2R')(OTf)2(DME) (R = ,6-diisopropylphenyl, 2,6-dichlorophenyl, or 2-tert-butylphenyl; R' = Me or Ph) with the lithium salt of various [beta]-diketonate and [beta]- diketiminates leads to complexes of the type Mo(NR)(CHCMe2R')(L)(OTf) (L = [beta]-diketonate or [beta]-diketiminate). Treatment of Mo(NR)(CHCMe2R')(L)(OTf) with NaBArf4 (Arf = 3,5- (CF3)2C6H3) in the presence of THF affords the cationic species {Mo(NR)(CHCMe2R')(L)(THF)}{BArf4}.

(cont.) The reactivity of the cationic [beta]-diketonate (acac) and [beta]-diketiminate (nacnac) complexes towards olefins has been examined, as has the thermal decomposition modes of the neutral and cationic nacnac complexes. Results demonstrate that the cationic species have short catalyst lifetimes, and that decomposition modes dominate the chemistry of several of the nacnac complexes. The X-ray crystal structures of several neutral and cationic complexes are reported. CHAPTER 4. Reaction of WCl3(OAr)3 (Ar = 2,6-diisopropylphenyl) with 4 equivalents of t-BuCH2MgCl in diethyl ether produces yellow crystalline W(C-t-Bu)(CH2-t-Bu)(OAr)2 in 40 - 50% isolated yield. The alkyl alkylidyne species reacts with 2-butyne and 3-hexyne in a metathetical fashion to generate the symmetric metallacyclobutadiene species, W(C3R3)(CH2-t-Bu)(OAr)2 (R = Me and Et, respectively). Replacement of the OAr ligands with LiNPh2 generates W(C-t-Bu)(CH2-t Bu)(NPh2)2 which serves as an in situ precursor to other dialkoxide species as demonstrated by alcoholysis with 1-adamantanol. The reaction between W(C-t-Bu)(CH2-t-Bu)(OAr)2 and benzonitrile generates the dimeric nitride species, [W(N)(CH2-t-Bu)(OAr)2]2.

(cont.) The nitride reacts with trimethylsilyl trifluoromethanesulfonate to afford the imido complex, W(NTMS)(CH2-t- Bu)(OAr)2(OTf), The X-ray crystal structure of W(C-t-Bu)(CH2-t-Bu)(OAr)2, [W(N)(CH2-t- Bu)(OAr)2]2, and W(NTMS)(CH2-t-Bu)(OAr)2(OTf) are reported as are studies concerning the catalytic efficiency of both W(C-t-Bu)(CH2-t-Bu)(OAr)2 and W(C-t-Bu)(CH2-t-Bu)(O-1- adamantyl)2. APPENDIX A. The reaction of Ph3P=CH2 with Mo(NAr)(CH-t-Bu)(O-t-BuF6)2 (Ar = 2,6-i-Pr2C6H3; O-t-BuF6 = OC(CF3)2Me) produces the anionic alkylidyne complex {Ph3PMe}{Mo(NAr)(C-t-Bu)(O-t- BuF6)2}. An X-ray structure determination of the complex reveals a bent Mo-N-C angle for the imido group, as expected when a metal-carbon triple bond is present. The reactivity of the anion towards electrophiles has been examined and shown to occur predominantly at the imido nitrogen.