Title: Unprecedented ROMP activity of low-valent rhenium-nitrosyl complexes : mechanistic evaluation of an electrophilic olefin metathesis system
Authors : Frech Nabold, Christian M.
Blacque, Olivier
Schmalle, Helmut W.
Berke, Heinz
Adlhart, Christian
Chen, Peter
Published in : Chemistry - A European Journal
Volume(Issue) : 12
Issue : 12
Pages : 3325
Pages to: 3338
Publisher / Ed. Institution : Wiley VCH
Publisher / Ed. Institution: Weinheim
Issue Date: 12-Apr-2006
License (according to publishing contract) : Licence according to publishing contract
Type of review: Peer review (Publication)
Language : English
Subjects : Reaction mechanisms; Ring-opening polymerization; Density functional calculations; Metathesis
Subject (DDC) : 540: Chemistry
660: Chemical engineering
Abstract: Rhenium bis-phosphine nitrosyl hydride complexes undergo protonation affording cationic unsatd. species, which exhibit high activity in metathetical ROMP polymn. of norbornene yielding in polynorbornene with high (Z)-double bond content; the cationic complexes also add diazoalkanes to give the corresponding carbenes. The reaction of hydrides [Re(H)(NO)2(PR3)2] (1a,b; R = PCy3, PiPr3) with [H(OEt2)2][BArF4] ([BArF4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) in benzene at room temp. gave the corresponding cations [Re(NO)2(PR3)2][BArF4] (2a,b). The addn. of phenyldiazomethane to benzene solns. of 2a,b afforded the moderately stable cationic rhenium(I)-benzylidene complexes [Re(NO)2(PR3)2(:CHPh)][BArF4] (3a,b) in good yields. The complexes 2a and 2b catalyze the ring-opening metathesis polymn. (ROMP) of highly strained non-functionalized cyclic olefins to give polymers with relatively high polydispersity indexes, high mol. wts. and over 80% (Z)-configuration of the double bonds in the chain backbone. However, these complexes do not show metathesis activity with acyclic olefins. The benzylidene derivs. 3a,b are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR expts. gave the first hints of the initial formation of carbene complexes from 2a,b and norbornene. In a detailed mechanistic study ESI-MS/MS measurements provided further evidence that the carbene formation is initiated by a unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylide-carbene complex, capable of undergoing metathesis with alternating rhenacyclobutane formation and cycloreversion reactions ("ylide" route). However, even at an early stage the ROMP propagation route is expected to merge into an "iminate" route by attack by the ylide function on one of the NNO atoms followed by phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. The proposed mechanism is supported further by detailed DFT calcns.
Departement: Life Sciences und Facility Management
Organisational Unit: Institute of Chemistry and Biotechnology (ICBT)
Publication type: Article in scientific Journal
DOI : 10.1002/chem.200501025
ISSN: 0947-6539
URI: https://digitalcollection.zhaw.ch/handle/11475/2111
Appears in Collections:Publikationen Life Sciences und Facility Management

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