Ethynyl[2.2]paracyclophanes and 4-isocyano[2.2]paracyclophane as ligands in organometallic chemistry

An alternative synthesis of (±)-4-ethynyl[2.2]paracyclophane (PCPCCH) (5) and 4,16-diethynyl[2.2]paracyclophane (6) via the Corey-Fuchs reaction has been developed. The olefinic intermediate 4-dibromovinyl[2.2]paracyclophane (3) has been isolated and structurally characterized. The racemic terminal alkyne 5 was employed as starting material for assembling of a luminescent extended π-conjugated system containing a thiophene unit and for a catalytic bis-silylation reaction yielding the olefinic dithioether Z-PhSCH₂Me₂SiC(H)C(PCP)SiMe₂CH₂SPh (9). The dimetallatetrahedran [Co₂(CO)₆(μ-η²-PCP-CCH)] (10) has been prepared and its crystal structure determined by an X-ray diffraction analysis. Alkyne 5 has also been used for the preparation of the Pt(0) complex [Pt(PPh₃)₂(PCPCCH)] (11) and the heterodinuclear dimetallacyclopentenone [(OC)₂Fe{μC(O)C(PCP)C(H)}(μ-dppm)Pt(PPh₃)] (12). The synthesis and reactivity of 4-isocyano[2.2]paracyclophane (15) towards heterobimetallic iron-platinum and palladium-platinum complexes is also presented. Opening of the dative iron → platinum bond of [(OC)₄Fe(μ-dppm)PtCl₂] (16) occurred upon addition of 15 to a CH₂Cl₂ solution of 16 leading to [(OC)₄Fe{μ-dppm}PtCl₂(CNPCP)] (17). Treatment of [ClPd(μ-dppm)₂PtCl] (18) with isocyanide 15 in a 1:1 ratio affords the A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)PtCl] (19), resulting from formal insertion of 15 into the Pd-Pt bond. Addition of 2 equiv. of 15-18 leads to the ionic A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)Pt(CNPCP)]Cl (20).