Affiliation:
1. Department of Chemistry University of British Columbia 2036 Main Mall Vancouver British Columbia V6T 1Z1 Canada
2. Department of Chemistry Simon Fraser University Burnaby British Columbia V5A 1S6 Canada
3. Centre for Molecular and Materials Science TRIUMF Vancouver British Columbia V6T 2A3 Canada
Abstract
AbstractUnderstanding free radical addition to multiple bonds is important to elucidating the mechanistic details of addition polymerization reactions, albeit the fleeting radical intermediates are very difficult to detect by conventional methodologies. Muon spin spectroscopy (μSR) is a highly sensitive method that can detect radical species at 106 spins (cf. EPR: 1012 spins, NMR: 1018 spins). Herein, we employ μSR to detect the radical‐addition products from three 1‐phosphabutadiene monomers, P‐analogues of isoprene. We show that muonium (Mu), a “light” H‐atom surrogate, adds predominantly at the C4 position of the P1=C2−C3=C4 moiety to give unprecedented 1‐phosphaallyl radicals as the major products. Our structural assignments are supported by assignment of muon, phosphorus and proton hyperfine coupling constants using DFT‐calculations. A minor radical product is also detected that is tentatively assigned to an PC3‐heterocyclic free radical. On the basis of DFT‐predictions, we speculate that its formation may involve initial addition of Mu+ at the C3 position followed by electron capture. These studies provide rare insights into the prospective radical (or cationic) polymerization of 1‐phosphabutadienes, which have previously been polymerized using anionic initiation.
Funder
Natural Sciences and Engineering Research Council of Canada
Subject
General Chemistry,Catalysis,Organic Chemistry