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Catalysts 2015, 5(4), 1928-1947; doi:10.3390/catal5041928

Molybdenum (VI) Imido Complexes Derived from Chelating Phenols: Synthesis, Characterization and ɛ-Caprolactone ROP Capability

1
Department of Chemistry, University of Hull, Hull HU6 7RX, UK
2
Chemistry Department, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK
*
Author to whom correspondence should be addressed.
Academic Editor: Keith Hohn
Received: 23 September 2015 / Revised: 20 October 2015 / Accepted: 2 November 2015 / Published: 12 November 2015
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization and ROP 2015)
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Abstract

Reaction of the bulky bi-phenols 2,2′-RCH[4,6-(t-Bu)2C6H2OH]2 (R = Me L1MeH2, Ph L1PhH2) with the bis(imido) molybdenum(VI) tert-butoxides [Mo(NR1)(NR2)(Ot-Bu)2] (R1 = R2 = 2,6-C6H3-i-Pr2; R1 = t-Bu, R2 = C6F5) afforded, following the successive removal of tert-butanol, the complexes [Mo(NC6H3i-Pr2-2,6)2L1Me] (1), [Mo(NC6H3i-Pr2-2,6)2L1Ph] (2) and [Mo(Nt-Bu)(μ-NC6F5)(L1Me)]2 (3). Similar use of the tri-phenol 2,6-bis(3,5-di-tert -butyl-2-hydroxybenzyl)-4-methylphenol (L2H3) with [Mo(NC6H3i-Pr2-2,6)2(Ot-Bu)2] afforded the oxo-bridged product [Mo(NC6H3i-Pr2-2,6)(NCMe)(μ-O)L2H]2 (4), whilst use of the tetra-phenols α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p- or -m-xylene L3pH4/L3mH4 led to {[Mo(NC6H3i-Pr2-2,6)2]2(μ-L3p)} (5) or {[Mo(NC6H3i-Pr2-2,6)2]2(μ-L3m)} (6), respectively. Similar use of [Mo(NC6F5)2(Ot-Bu)2] with L3pH4 afforded, after work-up, the complex {[Mo(NC6F5)(Ot-Bu)2]2(μ-L3p)}·6MeCN (7·6MeCN). Molecular structures of 1, 2·CH2Cl2, 3, 4·6MeCN, 6·2C6H14, and 7·6MeCN are reported and these complexes have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; for comparative studies the precursor complex [Mo(NC6H3i-Pr2-2,6)2Cl2(DME)] (DME = 1,2-dimethoxyethane) has also been screened. Results revealed that good activity is only achievable at temperatures of ≥100 °C over periods of 1 h or more. Polymer polydispersities were narrow, but observed molecular weights (Mn) were much lower than calculated values. View Full-Text
Keywords: molybdenum (VI); imido; phenolate; chelate; crystal structures; ε-caprolactone; ring opening polymerization molybdenum (VI); imido; phenolate; chelate; crystal structures; ε-caprolactone; ring opening polymerization
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Al-Khafaji, Y.; Prior, T.J.; Elsegood, M.R.J.; Redshaw, C. Molybdenum (VI) Imido Complexes Derived from Chelating Phenols: Synthesis, Characterization and ɛ-Caprolactone ROP Capability. Catalysts 2015, 5, 1928-1947.

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