Reaction of a Terminal Phosphinidene Complex with Azulenes: h 1 -Complexes, C H Bond Insertions, and 1,4-Adducts Rosa E. Bulo, [a] Andreas W. Ehlers, [a] Frans J. J. de Kanter, [a] Marius Schakel, [a] Martin Lutz, [b] Anthony L. Spek, [b] Koop Lammertsma,* [a] and Bing Wang [c] Introduction Two decades ago, Mathey and Marinetti [1] reported on the generation of the terminal phosphinidene complex [RPW(CO) 5 ] (Scheme 1) and its carbene-like reactivity toward olefins. Numerous reactions with double and triple bonds, leading to a plethora of novel ring structures, have subsequently shown the applicability of this transient re- agent with singlet electrophilic character. [2, 3] A striking difference between carbenes and electrophilic phosphinidene complexes is their reactivity towards aromat- ic compounds. For example, it is well known that the parent carbene DCH 2 reacts with benzene to give mainly the [1+2] cycloadduct norcaradiene, which rearranges to both cyclo- heptatriene and toluene, (Scheme 2); [4, 5] however, phosphin- idene complexes do not give such reactions. In fact, [RPW(CO) 5 ] is generated in solvents like toluene by chele- tropic elimination from 1, with release of an aromatic sub- strate. [1] Also, the attempted synthesis of uncomplexed phos- phepines is thwarted by expulsion of benzene from the pre- sumed phosphanorcaradiene intermediates (Scheme 3). [6] [a] Dr. R. E. Bulo, Dr. A. W. Ehlers, Dr. F. J. J. de Kanter, Dr. M. Schakel, Prof. Dr. K. Lammertsma Vrije Universiteit, FEW Department of Chemistry De Boelelaan 1083 1081 HV Amsterdam (The Netherlands) Fax: (+ 31) 20-444-7488 E-mail : lammert@chem.vu.nl [b] Dr. M. Lutz, Prof. Dr. A. L. Spek Bijvoet Center for Biomolecular Research Department of Crystal and Structural Chemistry Utrecht University (The Netherlands) [c] Dr. B. Wang Rhodia, Charleston, SC 29405 (USA) Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author. Cartesian coordi- nates, energies and thermal corrections of all stationary points. Scheme 1. Formation of phopshinidene complex 2 from a 7-phosphanor- bornadiene complex. Scheme 2. Reaction of methylene with benzene. Scheme 3. Formation and fragmentation of 7-phosphanorcaradiene. Abstract: Reaction of an in situ gener- ated phosphinidene complex [PhPW(CO) 5 ] with the aromatic azu- lene and guaiazulene leads to unex- pected 1,4-adducts of the seven-mem- bered ring and to C H bond insertion of the five-membered ring. A DFT analysis suggests that the reaction is in- itiated by formation of a h 1 -complex between the phosphinidene and the five-membered ring of the aromatic substrate. Four conformations of this complex were identified. Two convert without barrier to the slightly more stable syn- and anti-1,2-adducts. These undergo pericyclic 1,7-sigmatropic rear- rangements with remarkably low barri- ers to give 1,4-adducts, with an inverted configuration at the phosphorus center. An X-ray crystal structure is presented for one of the 1,4-adducts of guaiazu- lene. The other two h 1 -complexes insert with modest barriers into a C H bond of the five-membered ring. Keywords: azulenes ¥ density func- tional calculations ¥ electrophilic substitution ¥ phosphorus ¹ 2004 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim DOI: 10.1002/chem.200305711 Chem. Eur. J. 2004, 10, 2732 ± 2738 2732 FULL PAPER