FULL PAPER DOI:10.1002/ejic.201400046 CLUSTER ISSUE The Bimetallic Activation of White Phosphorus by trans- [RhCl(CO)(dppm)] 2 Results in a Tetrahedro-Rh 2 P 2 Moiety Maria Caporali,* [a] Luca Gonsalvi, [a] Vincenzo Mirabello, [a][‡] Andrea Ienco, [a] Gabriele Manca, [a] Fabrizio Zanobini, [a] and Maurizio Peruzzini* [a] Keywords: Metal–metal interactions / Phosphorus / Rhodium / Phosphine ligands The reaction of trans-[RhCl(CO)(dppm)] 2 with P 4 carried out at room temperature showed that bimetallic cooperation re- sulted in the cleavage of P 4 , giving a μ,η 2 -P 2 (μ-κ 2 :κ 2 -P 2 ) li- gand coordinated to the two metal centres. The new complex cis-[Rh 2 (CO) 2 (μ-dppm) 2 (μ,η 2 -P 2 )] has been fully character- ised in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction. The Rh–Rh distance of 2.723(18) Å is consistent with the presence of a metal–metal Introduction The selective chemical activation of white phosphorus is a subject of intense investigation by many research groups in both academic and applied fields. Metal-mediated acti- vation of P 4 has resulted in a spectacular variety of different P-topologies arising from the cleavage of one or more P–P bonds, and subsequent reassembly to afford M x P y moieties often endowed with further and frequently unexpected reac- tivity. [1] Recent results from our laboratories have shown that white phosphorus can be activated in a stepwise man- ner by different platinum group metals. In particular, the zig-zag P 6 chain in [Co(Ph 2 PCH 2 PPh 2 PPPPPh 2 PCH 2 - PPh 2 )]BF 4 (1), resulting from the initial activation of P 4 by Co(BF 4 ) 2 ·6H 2 O in the presence of dppm [dppm = 1,2- bis(diphenylphosphanyl)methane], [2] is further activated to give two separated zwitterionic diphenyl(alkyl)phos- phonium(+)diphosphenide(–) ligands, upon reaction of 1 with the complex [Pt(C 2 H 4 )(PPh 3 ) 2 ]. [3] Rhodium and irid- ium monocationic complexes [M(dppm) 2 ][OTf] also acti- vate P 4 , giving complexes such as [M(dppm)(PPh 2 CH 2 - PPh 2 PPPP)] + [M = Ir, 2a; Rh, 2b] by following a bimetallic activation pathway, with P 4 bridging two metal centres in an η 2 -fashion during an intermediate reaction step. [4] The [a] Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti OrganoMetallici (CNR-ICCOM), Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy E-mail: mperuzzini@iccom.cnr.it www.iccom.cnr.it [‡] Current address: Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201400046. Eur. J. Inorg. Chem. 2014, 1652–1659 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1652 single bond, which was supported by theoretical analysis showing that the HOMO of the complex has metal–metal bond character. A literature survey revealed that, in most cases, the P 2 unit acts as a P 2 4– ligand, and also in the case at hand the diphosphenyl ligand behaves as an eight-electron donor with all the π* combinations occupied and donates into four empty metal combinations. P 4 moiety of 2a and 2b may be further activated by reaction of these complexes with a Pt 0 precursor through cleavage of a P–P bond and coordination to Pt, resulting in the formation of new heterobimetallic complexes [M(dppm)(Ph 2 PCH 2 PPh 2 PPPP){Pt(PPh 3 ) 2 }]OTf {M = Ir (3a), Rh (3b)}. [5] A bimetallic activation pathway is also re- sponsible for the hydrolysis of P 4 , affording a variety of pol- yphosphanes [6] and hydroxyphosphanes [7] stabilised by {CpRu(PPh 3 ) 2 } moieties. Building on these examples of stepwise activation of P 4 by two different transition-metal moieties (Scheme 1), we investigated the direct activation of P 4 by a homobimetallic complex, namely the dimeric Rh I carbonyl complex [8] trans- [RhCl(CO)(dppm)] 2 (4), which is known to activate small molecules such as alkynes, [9] CO, [8c] and CS 2 . [10] Results and Discussion The reaction of the bimetallic complex 4 with two equiv- alents of P 4 was carried out in both dichloromethane and a mixture of methanol and tetrahydrofuran (THF) at room temperature, giving a yellow suspension within a few min- utes. On standing in MeOH/THF for some days, a dark- brown solution formed and yellow crystalline needles of the new bimetallic complex cis-[Rh 2 (CO) 2 (μ-dppm) 2 (μ,η 2 -P 2 )] (5; Scheme 2) separated out in 10% isolated yield. Complex 5 was obtained as a minor product from the reaction car- ried out in THF/methanol as described in the Experimental Section. It was fully characterised in solution by NMR, FTIR, and ESI mass spectrometry and in the solid state by single-crystal X-ray diffraction analysis (see Experimental Section for details).