Stepwise formation of an acetylide-bridged mixed-metal triangular dicobalt /iron cluster from [(OC) 4 Fe(PPh 2 CCPh)] Martin J. Mays a, *, Koshala Sarveswaran a , Gregory A. Solan b a Department of Chemistry, Lensfield Road, Cambridge CB2 1EW, UK b Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK Received 17 August 2002; accepted 19 February 2003 This paper is dedicated to Professor Brian Johnson, who has been a valued friend and colleague for many years Abstract Reaction of [(OC) 4 Fe(h 1 -PPh 2 CCPh)] (1) with [Co 2 (CO) 8 ] at room temperature affords the heterotrimetallic complex [(OC) 4 Fe(m- h 1 :h 2 -PPh 2 CCPh)Co 2 (CO) 6 ](2), in which the alkynic moiety in 1 is bound to a Co 2 (CO) 6 unit. Both the mono- and di-substituted complexes, [(OC) 4 Fe(m-h 1 :h 2 -PPh 2 CCPh)Co 2 (CO) 5 {P(OMe) 3 }] (3) and [(OC) 4 Fe(m-h 1 :h 2 -PPh 2 CCPh)Co 2 (CO) 4 {P(OMe) 3 } 2 ](4), are obtained on reaction of 2 with an excess of trimethylphosphite at elevated temperature; in both cases CO-substitution takes place solely at the cobalt centres. Thermolysis of 3 results in phosphorus-carbon bond cleavage and iron-cobalt bond formation to yield the mixed-metal 48-electron triangular cluster [FeCo 2 (CO) 6 {m 3 -h 2 -( Þ/)-CCPh}{P(OMe) 3 }(m-PPh 2 )] (5), in which a phenylacetylide ligand perpendicularly-bridges one of the iron-cobalt edges and a phosphido group bridges the cobalt-cobalt edge. Substitution of a cobalt carbonyl ligand occurs on reaction of 5 with triphenylphosphine to give [FeCo 2 (CO) 5 {m 3 -h 2 -( Þ/)-CCPh}{P(OMe) 3 }(PPh 3 )(m- PPh 2 )] (6). Single crystal X-ray diffraction studies have been performed on 2 and 6. # 2003 Elsevier B.V. All rights reserved. Keywords: Phosphinoalkyne; Mixed-metal; Iron; Cobalt; Cluster; Acetylide 1. Introduction The last thirty years have seen considerable research effort focused on the reactivity of phosphinoalkynes (R 2 PC  /CR, R /hydrocarbyl) towards binary metal carbonyl complexes. This can be attributed, in some measure, to the rich chemistry exhibited by the ligand as a result of its capacity to bind to a metal core through either the phosphorus centre or the alkynic unit or through both simultaneously [1 /5]. For example, treat- ment of PPh 2 C  /CPh with diiron nonacarbonyl gives the P-coordinated monometallic complex, [(OC) 4 Fe(h 1 - PPh 2 CCPh)] (1) and the alkyne-/P-coordinated bimetal- lic species [Fe 2 (CO) 6 (m:h 1 -h 2 -Ph 2 PCCPh) 2 ]. In addition, a third product can be isolated [Fe 2 (CO) 6 (m-PPh 2 )(m:h 2 - C 2 Ph)], in which scission of the P  /C(alkyne) bond has occurred to generate a bimetallic complex containing both diphenylphosphido (PPh 2 ) and phenylacetylide ( / C /CPh) ligands (Fig. 1) [6]. Indeed, phosphorus  / carbon bond cleavage of phosphino  /alkynes mediated by transition metals represents an important reactivity pattern and there are now numerous reports in which it has been identified [1,5  /9]. We have recently been interested in the chemistry of phosphinoalkynes and their application to the synthesis of mixed-metal complexes [10  /13]. In this regard complex 1 is particularly attractive since the P-coordi- nated ligand has a free alkynic donor site for coordina- tion to a different metal centre. Herein we report the stepwise synthesis of the triangular mixed-metal dicobalt  /iron cluster [FeCo 2 (CO) 6 {m 3 -h 2 -( Þ/)- CCPh}(P(OMe) 3 )(m-PPh 2 )] (5) via the complexation of a dicobalt unit to the alkynic moiety in 1. A similar strategy for cluster build-up involving the use of a phosphinoalkyne as an anchor for directing the forma- tion of homometallic clusters has been reported [14]. To * Corresponding author. Tel.:  /44-1223-336 343; fax:  /44-1223- 336 017. E-mail address: mjm14@cam.ac.uk (M.J. Mays). Inorganica Chimica Acta 354 (2003) 21  /28 www.elsevier.com/locate/ica 0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0020-1693(03)00316-5