Simple Synthesis of New Mixed Isocyanide-NHC-Platinum(II) Complexes and Their Catalytic Activity Christoph Hubbert, A Marcus Breunig, A Kristen J. Carroll, A Frank Rominger, A and A. Stephen K. Hashmi A,B A Organisch-Chemisches Institut, Universita ¨t Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany. B Corresponding author. Email: hashmi@hashmi.de Using the new modular and convergent approach to isocyanide-N-hetrocyclic carbene-platinum(II) complexes, eight new compounds have been synthesised. For three of these, detailed structural data could be obtained by X-ray crystal structure analyses. This new family of organoplatinum complexes is catalytically active for hydrosilylation reactions; styrene and phenylacetylene could be used as substrates; triethylsilane and 1,1,1,3,5,5,5-heptamethyltrisiloxane could be used as reagents. With some of the new platinum pre-catalysts, excellent regioselectivities of up to 98 : 2 could be obtained, and turnover numbers up to 840 were achieved. Manuscript received: 10 October 2013. Manuscript accepted: 3 December 2013. Published online: 23 January 2014. Introduction N-Hetrocyclic carbine (NHC) ligands have become one of the most important classes of ligands in catalysis. Among many others, [1] names like Bertrand, [2] Herrmann, [3] Grubbs, [4] Nolan, [5] Organ, [6] Glorius, [7] Straßner, [8] Fu ¨rstner, [9] Blechert, [10] Albrecht, [11] Grela, [12] and Crabtree [13] should be mentioned in this context. Further, NHC complexes are highly useful in many other fields of chemistry, like medical applications, [14] nanoparticles and supramolecular chemistry, [15] self-assembly, [16] photo- chemistry, [17] liquid crystals, [18] polymerisation, [19] and elec- tronically active materials [20] as recently summarised [21a] and highlighted. [21b] Although NHC ligands have a great number of advantages, the synthesis of saturated NHC complexes often remains chal- lenging and time-consuming. A widely used protocol starts with the formation of a bis-amine, either by substitution of a dihalide or by imine formation with subsequent reduction. [22] This diamine subsequently is converted into the corresponding imidazolinium salt by reaction with an ortho-ester. Although highly efficient, this method does not allow the formation of unsymmetrically substituted imidazolidene-derived NHCs. The route to unsymmetrically substituted imidazolidene NHCs is limited to certain substituents. [23] Isocyanide–metal complexes have been employed fre- quently for the formation of acyclic or even cyclic carbenes. [24] The activation of the coordinated isocyanide for an inter- or intramolecular attack by a nucleophile represents the basic principle of this approach. The nature of the nucleophile determines whether the reaction leads to the formation of acyclic or cyclic carbenes. Based on these methods, N,O- as well as N,N- heterocyclic carbenes have been synthesised by intramolecular ring closure (the latter were obtained in low yields only). This method delivers NHCs unsubstituted at nitrogen and only alkyl substituents could be attached to the nitrogen atom subsequ- ently. [25] The synthesis of NHC complexes by template synthe- sis, which is shorter than the procedure mentioned above, has been summarised by Hahn. [26] The preparation of unsymmetrically N,N 0 -disubstituted imidazolidene-NHC complexes derived from isocyanide pre- cursors has been published recently. [27] Like Hahn’s synthesis, this is a template synthesis, but the assembly of the NHC-metal complex from three different precursors in one step makes the method highly convergent and allows the fast synthesis of libraries with a broad diversity by using this modular approach. The method worked nicely for gold(I), [28] palladium(II), [29] and even two examples for platinum(II) were reported. In the case of the latter two metals, the bis-isocyanide complexes were selec- tively converted into the mixed isocyanide-NHC complexes. Although the activity of the new isocyanide-NHC-palladium(II) complexes in cross-coupling reactions with aryl chlorides has been studied, [30] the catalytic activity of the new and previously unknown isocyanide-NHC-platinum(II) complexes has not been investigated so far. As related NHC-Pt II complexes have been used in catalysis, [31] the present paper now, for the first time, discusses the catalytic activity of this new class of organometa- llic compounds, the isocyanide-NHC-platinum(II) complexes. The hydrosilylation of C–C multiple bonds with platinum- based catalysts is an important reaction for the production of intermediates for silicon-based polymers. For this reaction, classical systems such as the Karstedt [32] or the Speier [33] cata- lysts show very high activity; however, this is accompanied by the fairly rapid formation of inactive colloidal platinum. The devel- opment of new hydrosilylation catalysts is thus still of interest, and many alternative catalysts have been reported. [34] Recently, platinum complexes containing N-heterocyclic carbene ligands CSIRO PUBLISHING Aust. J. Chem. 2014, 67, 469–474 http://dx.doi.org/10.1071/CH13546 Journal compilation Ó CSIRO 2014 www.publish.csiro.au/journals/ajc Full Paper RESEARCH FRONT