Synthesis of (1-Adamantylimido)vanadium(V) Complexes Containing Aryloxo, Ketimide Ligands: Effect of Ligand Substituents in Olefin Insertion/Metathesis Polymerization

Abstract

A series of (1-adamantylimido)vanadium(V) complexes containing anionic donor ligands of the type, V(NAd)Cl2(L) [Ad = 1-adamantyl; L = O-2,6-Me2C6H3 (2), O-2,6-(i)Pr2C6H3 (3), NC(t)Bu2 (5), NC((t)Bu)CH2SiMe3 (6), NC((t)Bu)Ph (7), NCPh2 (8)], have been prepared from V(NAd)Cl 3, which was in turn prepared from VOCl3 by treatment with 1-adamantylisocyanate in octane, by treatment with the corresponding lithium salts (lithium phenoxides, lithium ketimides) in Et2O. These complexes (2, 3, 5-8) were identified by NMR spectroscopy and elemental analysis, and the structures for 2 and 5 were determined by X-ray crystallography. The reaction of V(NAd)Cl3 with 2,6-dimethylphenol in n-hexane afforded the tris(aryloxo) analogue V(NAd)(O-2,6-Me2C6H3)3 (4), the structure of which was determined by X-ray crystallography. 8 gradually decomposed in toluene to give a dimeric species, [N(Ad)H3](+)[V2(mu2-Cl)3Cl2(NAd)2(NCPh2)2](-) (10), but 8 was stabilized as a PMe 3 coordinated species, V(NAd)Cl2(NCPh2)(PMe3)2 (9): the structures for 9 and 10 were determined by X-ray crystallography. These complexes were evaluated as catalyst precursors for ethylene polymerization in the presence of MAO. The ketimide analogues, especially 5, exhibited moderate catalytic activity, and the activity with a series of V(NAd)Cl2(L)-MAO catalyst systems increased in the order: L = NC(t)Bu2 (5, 516 kg-PE/mol x V x h) > NC((t)Bu)Ph (7, 300) > NCPh2 (8, 105) > NC((t)Bu)CH2SiMe3 (6, 70.8). These complexes (2, 3, 5, 6) were found to be effective as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of MeMgBr and PMe3.

(Imido)vanadium Complexes as Efficient Catalyst Precursors for Olefin Polymerization/Oligomerization

“…We recently reported that (arylimido)vanadium(V) complexes containing anionic donor ligands, V(NAr)Cl 2 (L) [Ar = 2,6-Me 2 C 6 H 3 ; L = N=C t Bu 2 , OAr 0 ], exhibited notable activities for ethylene (co)polymerization in the presence of Al cocatalysts, affording ultra high molecular weight (co)polymers with uniform molecular weight distributions [13,[47][48][49][50][51][52][53][54][55][56]. These vanadium(V)-dichloride complexes, V(NAr)Cl 2 (L) [Ar = 2,6-Me 2 C 6 H 3 ; L = aryloxo] (1) [12,13], ketimide (2) [53,73], phenoxy-imine (3) [54], (2-anilidomethyl)pyridine (4) [55] or V(NAd)Cl 2 (L) [Ad = 1-adamantyl; L = aryloxo (5), ketimide (6)] [56], could be prepared by treating V(NAr)Cl 3 with the corresponding lithium salts (such as LiN=C t Bu 2 , LiOAr, etc.)…”

“…These vanadium(V)-dichloride complexes, V(NAr)Cl 2 (L) [Ar = 2,6-Me 2 C 6 H 3 ; L = aryloxo] (1) [12,13], ketimide (2) [53,73], phenoxy-imine (3) [54], (2-anilidomethyl)pyridine (4) [55] or V(NAd)Cl 2 (L) [Ad = 1-adamantyl; L = aryloxo (5), ketimide (6)] [56], could be prepared by treating V(NAr)Cl 3 with the corresponding lithium salts (such as LiN=C t Bu 2 , LiOAr, etc.) in Et 2 O or toluene (Scheme 1).…”

“…The crystallographic results revealed that the ketimide-dichloride analogue, V(NAr)Cl 2 (N=C t Bu 2 ) (2a), folds a distorted tetrahedral geometry around V, and the complex (2a) is a 14 electron species [73]. Note that these complexes are effective catalyst precursors for ethylene (co)polymerization in the presence of Al cocatalysts [47][48][49][50][51][52][53][54][55][56][57]. In particular, the aryloxo analogues (1) showed the notable activities for ethylene polymerization especially in the presence of halogenated Al alkyls (Et 2 AlCl, Me 2 AlCl, EtAlCl 2 , etc.…”

“…Therefore, design and synthesis of new vanadium complex catalysts for the controlled polymerization are one of the most important subjects in this research area [2,3,[11][12][13]. Although there are many recent reports especially with vanadium(III) and vanadium(IV) complexes for the above purpose [11][12][13], we focused on high oxidation state (imido)vanadium(V) complexes containing anionic ancillary donor ligands [13,[47][48][49][50][51][52][53][54][55][56][57]. This is because that olefin coordination into the highest oxidation state vanadium(V)-alkyl complexes would be suited for the subsequent insertion [57].…”

“…In this paper, we wish to summarize our recent results concerning design and synthesis of (imido)vanadium(V) complex catalysts for both olefin coordination insertion and olefin metathesis polymerization [13,[47][48][49][50][51][52][53][54][55][56][57][73][74][75][76]. Moreover, we also introduce our results for efficient selective ethylene dimerization using vanadium(V) complexes containing (2-anilidomethyl)pyridine ligand [77].…”