Synthesis, reactions, and DFT studies of macrocycle-supported imido titanium alkyl cations derived from Ti(N t Bu)(Me 3 [9]aneN 3 )R 2 (R ) Me (1) or CH 2 SiMe 3 (2)) are described (Me 3 [9]aneN 3 ) 1,4,7trimethyltriazacyclononane). Reaction of 1 with 1 equiv of [Ph 3 C][BAr F 4 ] or BAr F 3 (Ar F ) C 6 F 5 ) in C 6 D 5 Br afforded the methyl cation [Ti(N t Bu)(Me 3 [9]aneN 3 )Me] + (6 + ), whereas with half an equivalent of [Ph 3 C][BAr F 4 ] the fluxional methyl-bridged homo-binuclear cation [Ti 2 (N t Bu) 2 (Me 3 [9]aneN 3 ) 2 Me 2 (µ-Me)] + (10 + ) was formed. Reaction of 1 with [Ph 3 C][BAr F 4 ] in CD 2 Cl 2 formed the monochloride cation [Ti(N t Bu)(Me 3 [9]aneN 3 )Cl] + (8 + ), which was also prepared from Ti(N t Bu)(Me 3 [9]aneN 3 )Cl(Me) and [Ph 3 C][BAr F 4 ]. Cation 8 + reacted with pyridine to give the adduct [Ti(N t Bu)(Me 3 [9]aneN 3 )Cl(py)] + (9 + ) and with Ti(N t Bu)(Me 3 [9]aneN 3 )Me 2 to form the chloride-bridged cation [Ti 2 (N t Bu) 2 (Me 3 [9]aneN 3 ) 2 -Me 2 (µ-Cl)] + (11 + ). Reaction of 2 with [Ph 3 C][BAr F 4 ] gave [Ti(N t Bu)(Me 3 [9]aneN 3 )(CH 2 SiMe 3 )] + (7 + ), which is stabilized by a β-Si-C agostic interaction characterized by a high-field-shifted 29 Si NMR resonance. Attempts to generate 7 + by reaction of 2 with [PhNMe 2 H][BAr F 4 ] in CH 2 Cl 2 led to Ti(N t Bu)(Me 3 [9]aneN 3 )Cl 2 and [PhNMe 2 (CH 2 Cl)][BAr F 4 ] (12-BAr F 4) via a series of solvent activation reactions, the details of which have been elucidated. Reaction of 6 + or 7 + with Ph 3 PO afforded the adducts [Ti(N t Bu)(Me 3 [9]aneN 3 )R(Ph 3 PO)] + , whereas with pyridine a C-H bond activation reaction occurred to give [Ti(N t Bu)(Me 3 [9]aneN 3 )(NC 5 H 4 )] + (17 + ) and the corresponding alkane RH. Density functional theory calculations of the isolobal d 0 fragments [Ti(NR)(R′ 3 [9]aneN 3 )] 2+ and [Cp 2 Ti] 2+ found that their frontier orbitals, although broadly similar, featured important differences in their shapes and energies. These account for the absence of any R-C-H agostic interaction in 6 + , whereas [Cp 2 TiMe] + is stabilized by a weak interaction of this type, as judged by DFT-computed geometries. The experimentally observed increase in Ti-Me group average 1 J CH on forming either 6 + from 1 or [Cp 2 TiMe] + from Cp 2 TiMe 2 is reproduced by DFT and attributed to intrinsic global changes in carbon 2s orbital contribution to the Ti-C and C-H bonds upon cation formation. These changes were shown to mask the otherwise expected decrease in average 1 J CH for the R-agostic methyl in [Cp 2 TiMe] + . The difference between the Ti-Me 1 J CH values in 1 (111 Hz) and isolobal Cp 2 TiMe 2 (124 Hz) was also attributed to differences in Ti center electrophilicity. The experimental high-field-shifted 29 Si NMR resonance in 7 + was well reproduced in the DFT-computed β-Si-C agostic structure, and upper and lower limits for the strength of the agostic interaction were estimated. An NBO analysis of the Ti-CH 2 SiMe 3 bonding found several different contributions, including negative hyperconjugation (populat...

A family of ca. 50 imidotitanium precatalysts [Ti(NR)(Me(3)[9]aneN(3))Cl(2)](R = alkyl or aryl; Me(3)[9]aneN(3)= 1,4,7-trimethyltriazacyclononane) were prepared in good yields using semi-automated procedures; high-throughput screening techniques identified seven highly active ethylene polymerisation precatalysts with activities in the range ca. 3 400 to 10 000 kg(PE) mol(-1) h(-1) bar(-1).

A combined experimental and DFT study of the reactions of the titanium imido methyl cation [Ti(NtBu)(Me3[9]aneN3)Me]+ (4+) with AlMe3 and ZnMe2 is described. Reaction of 4+ with AlMe3 gave [Ti(NtBu)(Me3[9]aneN3)(mu-Me)2AlMe2]+ (7+), the first structurally characterized AlMe3 adduct of a transition metal alkyl cation and a model for the presumed resting state in MAO-activated olefin polymerizations. Reaction of 4+ with ZnMe2 also gave a methyl-bridged heterobinuclear species, namely [Ti(mu-NtBu)(Me3[9]aneN3)(mu-Me)2ZnMe]+ (8+), the first directly observed ZnMe2 adduct of a transition metal alkyl cation. At room temperature, all three metal-bound methyls of 8+ underwent rapid exchange with those of free ZnMe2, whereas at 233 K only the terminal Zn-Me group exchanged significantly. Addition of AlMe3 to 8+ quantitatively formed 7+ and ZnMe2. Reaction of 4+ with Cp2ZrMe2 gave [Ti(NtBu){Me2(mu-CH2)[9]aneN3}(mu-CH2)ZrCp2]+ (10+) via a highly selective double C-H bond activation reaction in which both alkyl groups of Cp2ZrMe2 were lost. DFT calculations on models of 7+ confirmed the approximately square-based pyramidal geometries for the bridging methyl groups. Calculations on 8+ found that the formation of the Ti(mu-Me)2Zn moiety is assisted by an Nimide-->Zn dative bond. DFT calculations for the sterically less encumbered methyl cation [Ti(NMe)(H3[9]aneN3)Me]+ found strong thermodynamic preferences for adducts featuring Nimide-->M (M = Al or Zn) interactions. This offers insight into recently observed structure-productivity trends in MAO-activated imido-based polymerization catalysts. Calculations on the metallocenium adducts [Cp2Ti(mu-Me)2AlMe2]+ and [Cp2Ti(mu-Me)2ZnMe]+ are described, each showing alpha-agostic interactions for the bridging methyl groups. For these systems and the imido ones, the coordination of AlMe3 to the corresponding monomethyl cation is ca. 30 kJ mol-1 more favorable than for ZnMe2.

Dedicated to Professor Richard R. Schrock on the occasion of his 60 th birthday in appreciation of his many contributions to organometallic chemistry.Abstract: Transition metal imido compounds having the general formula [(L) n M(NR)] [where (L) n is a supporting ligand or ligand set, and R typically is alkyl or aryl] have been known for nearly 50 years, and during the last two decades have been the focus of considerable attention. Relatively recently their potential application in the Ziegler-Natta polymerisation of olefins has been realised. In this contribution we review the Ziegler-Natta polymerisation of olefins by transition metal imido compounds. A general introduction to homogeneous Ziegler-Natta olefin polymerisation and key aspects of transition metal imido chemistry is given, followed by a short description of a related imidobased polymerisation process, namely ring-opening olefin metathesis polymerisation catalysed by imidosupported molybdenum and tungsten alkylidenes. A summary of the "design principles" that have been employed in the development of certain imido-based Ziegler-Natta catalysts is presented, followed by a comprehensive survey of the literature in the title area.

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A comprehensive account of the synthesis, properties, and evaluation of a wide range of ethylene homopolymerization catalysts derived from imido titanium compounds supported by the triazacyclic ligands Me 3 [9]aneN 3 and R 3 [6]aneN 3 is described (Me 3 [9]aneN 3 ) 1,4,7-trimethyltriazacyclononane; R 3 [6]aneN 3 ) 1,3,5-trimethyl-or 1,3,5-tris(n-dodecyl)triazacyclohexane). Conventional preparative-scale reactions afforded the triazacycle-supported imido titanium compounds Ti(NR)(Me 3 [9]aneN 3 )Cl 2 (R ) t Bu (1), 2,6-C 6 H 3 Me 2 , 2,6-C 6 H 3 i Pr 2 , Ph, C 6 F 5 , or CH 2 Ph (6)). Solid phase-supported analogues of 1 and 6 (linked by either the macrocycle or imido ligand to a 1% cross-linked polystyrene support) and representative Me 3 [6]aneN 3 solution phase systems Ti(NR)(R 3 [6]aneN 3 )Cl 2 (R ) Me or n-dodecyl) were also synthesized. At ambient temperature, solution phase Me 3 [9]aneN 3 catalyst systems were more active for ethylene polymerization (methyl aluminoxane (MAO) cocatalyst) than their solid phase-supported or Me 3 [6]aneN 3 analogues. A library of 41 other triazacyclononane-supported catalysts was prepared by the semiautomated, sequential treatment of Ti(NMe 2 ) 2 Cl 2 with RNH 2 and Me 3 [9]aneN 3 . The ethylene polymerization capabilities of 46 compounds of the type Ti(NR)(Me 3 [9]aneN 3 )Cl 2 were evaluated at 100°C (MAO cocatalyst) and compared in representative cases to the corresponding productivities at ambient temperature. Whereas either bulky N-alkyl or N-aryl imido substituents in the compounds Ti(NR)(Me 3 [9]aneN 3 )Cl 2 were sufficient to give highly active catalysts at ambient temperature, only those with bulky N-alkyl groups excelled at 100°C. Polymer end group analysis indicated that polymeryl chain transfer to both AlMe 3 and ethylene monomer is an active mechanism in these systems. The use of MAO pretreated with BHT-H (BHT-H ) 2,6-di-tert-butyl-4-methylphenol) led to higher productivites, increased polymer molecular weights, and more polymer chain unsaturations, but productivity decreased when a large excess of BHT-H was used.

A series of alkyl- and aryl-imido titanium dialkyl compounds Ti(NtBu)(Me3[9]aneN3)R2 (R = Me (1), CH2SiMe3 (3), CH2 tBu (4), CH2Ph (5)), Ti(NR)(Me3[9]aneN3)Me2 (R = iPr (6), Ph (7), 3,5-C6H3(CF3)2 (8), 2,6-C6H3 iPr2 (9), 2-C6H4CF3 (10), 2-C6H4 tBu (11)), and Ti(NR)(Me3[9]aneN3)(CH2SiMe3)2 (R = iPr (12), ArF (13)) were prepared and crystallographically characterized in the case of 1, 6−9, and 11 (Me3[9]aneN3 = 1,4,7-trimethyl triazacyclononane; ArF = C6F5). These compounds, isolobal with the titanocenes Cp2TiR2, were thermally stable at elevated temperatures except for 4. Reaction of 7 with [Ph3C][BArF 4] (TB) and diisopropylcarbodiimide in CH2Cl2 gave the Ti−Me insertion product [Ti(NPh)(Me3[9]aneN3){MeC(NiPr)2}][BArF 4] (15-BAr F 4 ). The corresponding reaction of 7 in the absence of organic substrate gave [Ti2(μ-NPh)2(Me3[9]aneN3)2Cl2][BArF 4]2 via a solvent activation reaction. The room-temperature ethylene polymerization capabilities of the dialkyl compounds were evaluated using TB cocatalyst in the presence of AliBu3 (TIBA). Among the dimethyl precatalysts, only the systems 1 and 11, with the bulkiest imido groups, showed high productivities (6230 and 1210 kg mol-1 h-1 bar-1, respectively). The productivites of the other tert-butyl imido precatalysts 3 and 4 (130 and 120 kg mol-1 h-1 bar-1, respectively) were substantially lower than that of 1. The catalyst system 1/TIBA (2500 equiv, no added TB) was also active for ethylene polymerization (225 kg mol-1 h-1 bar-1). The less productive imido dialkyl precatalysts all formed complex mixtures on exposure to TIBA. The polyethylenes produced with 1, 3, and 5−11 generally had M w/M n values in the range 2.6−3.0. The PE formed with 1/TB/TIBA was terminated only by methyl end groups, consistent with chain transfer to TIBA followed by subsequent β-H transfer by the resultant titanium isobutyl cation. The alkyl cations [Ti(NtBu)(Me3[9]aneN3)R]+ (R = Me or CH2SiMe3) reacted rapidly with TIBA in C6D5Br at −30 °C, forming isobutene. DFT calculations found that TIBA adducts of the model methyl cation [Ti(NMe)(H3[9]aneN3)Me]+ were energetically favorable by ca. −80 to −110 kJ mol-1. Whereas 1 alone or with AlMe3 present has been shown to form only Ph3CMe on reaction with [Ph3C]+, 1:1 mixtures of 1 and TIBA gave Ph3CH as the only trityl-containing product, suggesting a key role for transient [AliBu2]+ in the activation process for these catalysts. Overall, the imido group in the Ti(NR)(Me3[9]aneN3)Me2/TB/TIBA catalysts systems appears to have two roles:  to stabilize the dialkyl precatalyst toward degradation by the TIBA itself prior to activation, and to inhibit the formation of catalytically inactive hetero- or homo-bimetallic complexes.

The carbonylruthenium(0) complex Ru(CO){PCyp 2 (η 2 -C 5 H 7 )} 2 (4) has been prepared by reaction of RuH 2 {PCyp 2 (η 2 -C 5 H 7 )} 2 (3) with an excess of tert-butylethylene in the presence of ethanol. Decarbonylation of ethanol is also observed when reacting the bis(dihydrogen) complex RuH 2 (η 2 -H 2 ) 2 (PCyp 3 ) 2 (1) with 2 equiv of ethanol. The reaction results formally in the substitution of one dihydrogen ligand by a carbonyl, and the corresponding complex RuH 2 (η 2 -H 2 )(CO)(PCyp 3 ) 2 (5) was isolated. An excess of tert-butylethylene reacted with 5 to give RuH 2 (CO){PCyp 2 (η 2 -C 5 H 7 )}(PCyp 3 ) (6), which corresponds to the formal loss of 2 equiv of dihydrogen: loss of the dihydrogen ligand and dehydrogenation of one cyclopentyl ring. The dihydride 6 can be dehydrogenated further by reaction with ethylene, affording the ruthenium(0) complex Ru(η 2 -C 2 H 4 )(CO){PCyp 2 (η 2 -C 5 H 7 )}(PCyp 3 ) (7). Finally, the dicarbonyl complex RuH 2 (CO) 2 (PCyp 3 ) 2 (8) was isolated by exposing 1 to 3 bar of CO. 8 and the new complexes 4-7, resulting from partial dehydrogenation of one or two cyclopentyl rings of the tricyclopentylphosphines and/or decarbonylation of alcohol, were characterized by multinuclear NMR, IR, elemental analysis, and X-ray diffraction.