Carbyne complex rhenium

The rhenium carbyne complex Re(=CCMe3)(=NAr)(OR)2 is active for metathesis of internal acetylenes when OR is OCMe(CF3)2, but not when OR is OCMe2CF3, OCMe3 or OC6H3-i-Pr2-2,65 6. The complex W(=CMe)(Cl)(PMe3)4 undergoes stoichiometric metathesis with PhC=CPh but the product PhC=CMe remains coordinated to the metal centre759. 

The cycloaddition of imines to the metal-carbon triple bond in the cationic rhenium carbyne complex 263 was reported by Geoffroy and... 

Somewhat related are the reactions of the rhenium carbyne complex 263 with nitroso compounds (40,198). Reaction of the tetrachloroborate salt... 

The rhenium carbyne complex Re(=CCMe3)(=NAr)[OCMe(CF3)2]2 is active for metathesis of internal acetylenes, but analogous complexes, where OR is OCMe2(Cp3), OCMe3, or OC6H3-/-Pr2-2,6, are not active the rhenium centre is insufficiently electrophilic to enable the acetylenic substrate to overcome the barrier to reaction (Schrock 1988d Weinstock 1991). 

Dihalocarbene complexes are useful precursors to new carbenes by nucleophilic displacement of the chlorine substituents. This has been nicely illustrated for Fe(TPP)(=CCl2) by its reaction with two equivalents of Re(CO)5J to give the unusual /t-carbido complex Fe(TPP)=C=Re(CO)4Re(CO)5 which also contains a rhenium-rhenium bond. " The carbido carbon resonance was observed at 211.7 ppm in the C NMR spectrum. An X-ray crystal structure showed a very short Fe=C bond (1.605(13) A, shorter than comparable carbyne complexes) and a relatively long Re=C bond (1.957( 12) A) (Fig. 4, Table III). " ... 

The lability of the N2 ligand towards alkyl and aryl isocyanides has been demonstrated by equation (2) which occurs readily with both alkyl and aryl isocyanides.40 The resulting complexes are electron rich , the alkyl isocyanide derivatives ReCl(CNR)(dppe) (R = Me or Bul) undergoing electrophilic attack upon treatment with HBF4 to form the carbyne complexes trcms-[ReCl(CNHR)(dppe)2]BF4.41 Other noteworthy features of the series of complexes ReCl(CNR)(dppe)2 and ReCl(CNAr)(dppe)2, are the low value of v(CN), the presence of a bent M—CNR coordination mode, and their ease of oxidation (as measured by cyclic voltammetry) to the corresponding rhenium(II) monocations.40... 

The basicity at the 3-carbon is illustrated by the reactions in Equations 13.26 and 13.27. Reaction of the octahedral rhenium vinylidene in Equation 13.26 with HBF generates the cationic carbyne complex from addition of a proton to the basic 3-carbon. Because low-valent metals are often basic, addition of a proton to the vinylidene 3-carbon is likely to occur by a multi-step process initiated by protonation of the metal center. This initial protonation at the metal center would then be followed by migration of the proton to the 3-carbon. The reaction of acid with the iridium vinylidene in Equation 13.27 illustrates this mechanism. In this case, protonation first generates an iridium-hydride complex. The hydride in this complex tlien migrates to the p-carbon to generate an alkylidyne complex. ... 

CHEMISTRY AND ELECTROCHEMISTRY OF ALKYNE- AND ISOCYANIDE-DERIVED CARBYNE COMPLEXES OF RHENIUM, MOLYBDENUM OR TUNGSTEN... 

ALKYNE-DERIVED CARBYNES 2.1. Rhenium Phosphinic Complexes... 

We have shown that carbyne complexes of rhenium can be conveniently prepared by 3-protonation at vinylidene ligands [5], a route which has been described for other systems [6]. The vinylidene species have been obtained by 1,2-hydrogen shift at 1-alkynes (HCeCR) when activated by an electron-rich d Re centre, typically trans- ReCl (dppe) 2 (dppe=Ph2PCH2CH2PPh2) provided by a parent dinitrogen complex [5]. 

Synthesis and characterisation of the first organometallic Tc(VIII) complex [MeTcOs] is described. Its reactions with alkenes and with aromatic amine bases are different to those of the analogous rhenium complex. 25 Terminal alkynes react with [Tc(Cl)(dppe)2] to form vinylidene complexes [Tc(=C=CHR)(Cl)(dppe)2] (R = Ph, Me, Bu ). Treatment of these complexes with acid yields the respective carbyne complexes [Tc( CH2R)(Cl)(dppe)2]. The Tc-C bond lengths in these complexes vary form 1.861(9) to 1.724(7) A, 26... 

E. O. Fischer and W. Schambeck, /. Organomet. Chem., 1980, 201, 311. Ketene-iminyl complexes of manganese and rhenium formed by addition of isocyanides to cationic carbyne complexes. 

The acetylide complex [Co2(CO)6 U-PhC=CRe(CO)5 ] (256) (obtained by the treatment of the binuclear acetylide-hydride carbonyl complex of rhenium [Re2(CO)g( -H)( -C CPh)] with [Co2(CO)g] undergoes nondestructive reaction with oxygen resulting in the net loss of one acetylide carbon atom together with a CO ligand and formation of the carbyne cluster complex [Co2Re(CO)io(/i3-CPh)] (257) (Scheme 68), ... 

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