A series of alkyl- and aryl-imido titanium dialkyl compounds Ti(N
tBu)(Me
3[9]aneN
3)R
2 (R = Me (
1),CH
2SiMe
3 (
3), CH
2tBu (
4), CH
2Ph (
5)), Ti(NR)(Me
3[9]aneN
3)Me
2 (R =
iPr (
6), Ph (
7), 3,5-C
6H
3(CF
3)
2(
8), 2,6-C
6H
3iPr
2 (
9), 2-C
6H
4CF
3 (
10), 2-C
6H
4tBu (
11)), and Ti(NR)(Me
3[9]aneN
3)(CH
2SiMe
3)
2 (R =
iPr(
12), Ar
F (
13)) were prepared and crystallographically characterized in the case of
1,
6-
9, and
11 (Me
3[9]aneN
3 = 1,4,7-trimethyl triazacyclononane; Ar
F = C
6F
5). These compounds, isolobal with the titanocenesCp
2TiR
2, were thermally stable at elevated temperatures except for
4. Reaction of
7 with [Ph
3C][BAr
F4](TB) and diisopropylcarbodiimide in CH
2Cl
2 gave the Ti-Me insertion product [Ti(NPh)(Me
3[9]aneN
3){MeC(N
iPr)
2}][BAr
F4] (
15-BArF4). The corresponding reaction of
7 in the absence of organicsubstrate gave [Ti
2(
![](/images/entities/mgr.gif)
-NPh)
2(Me
3[9]aneN
3)
2Cl
2][BAr
F4]
2 via a solvent activation reaction. The room-temperature ethylene polymerization capabilities of the dialkyl compounds were evaluated using TBcocatalyst in the presence of Al
iBu
3 (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
-1h
-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 productiveimido dialkyl precatalysts all formed complex mixtures on exposure to TIBA. The polyethylenes producedwith
1,
3, and
5-
11 generally had
Mw/
Mn values in the range 2.6-3.0. The PE formed with
1/TB/TIBAwas terminated only by methyl end groups, consistent with chain transfer to TIBA followed by subsequent
![](/images/gifchars/beta2.gif)
-H transfer by the resultant titanium isobutyl cation. The alkyl cations [Ti(N
tBu)(Me
3[9]aneN
3)R]
+ (R= Me or CH
2SiMe
3) reacted rapidly with TIBA in C
6D
5Br at -30
![](/images/entities/deg.gif)
C, forming isobutene. DFT calculationsfound that TIBA adducts of the model methyl cation [Ti(NMe)(H
3[9]aneN
3)Me]
+ were energeticallyfavorable by ca. -80 to -110 kJ mol
-1. Whereas
1 alone or with AlMe
3 present has been shown to formonly Ph
3CMe on reaction with [Ph
3C]
+, 1:1 mixtures of
1 and TIBA gave Ph
3CH as the only trityl-containing product, suggesting a key role for transient [Al
iBu
2]
+ in the activation process for these catalysts.Overall, the imido group in the Ti(NR)(Me
3[9]aneN
3)Me
2/TB/TIBA catalysts systems appears to havetwo 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.