Cr-Acetylide complexes

The effect of stoichiometry, substituent, and temperature were investigated in reactions between the hydride HCo(tdppep) (19) and a number of alkynes.175 The cr-acetylide complex (20) and the (7-alkenyl (21) are formed from the stoichiometric reaction with ethyl propiolate. However, when a ten-fold excess of ethyl propiolate is used, the acetylide complex is formed quantitatively and one equivalent of alkyne is hydrogenated to alkene. Forcing conditions and a large excess of... 

Cationic vinylidene complexes bearing a -hydrogen are readily depro-tonated to give the corresponding neutral cr-acetylide complexes ... 

Several other research groups have described NLO studies with Ru cr-acetylide complexes [132-139], Gimeno and co-workers have prepared a number of indenyl complexes, including heterobinuclear species, with Ru ( i75-C9H7)(PPh3)2 +... 

A series of alkynyl complexes TpRu(C=CR)Cl(NO) were prepared by Onishi et al. from TpRuCl2(NO) and an excess of terminal alkynes in the presence of NEts (Scheme 21)."° If the same reaction is performed with ethynylbenzene in the presence of Cul as catalyst, the novel bis(alkynyl) complex TpRu(C=CPh)2(NO) was obtained. " Upon treatment of these cr-acetylide complexes with one equivalent of H2O in the presence of HBF4 Et20 in distilled MeOH several compounds were obtained in good yields including ketonyl, bisketonyl, acyl and metallacyclopente-none complexes. 

The chemistry of metal complexes featuring alkyne and alkynyl (acetylide) ligands has been an area of immense interest for decades. Even the simplest examples of these, the mononuclear metal acetylide complexes L MC=CR, are now so numerous and the extent of their reaction chemistry is so diverse as to defy efforts at a comprehensive review. " The utility of these complexes is well documented. Some metal alkynyl complexes have been used as intermediates in preparative organic chemistry and together with derived polymeric materials, many have useful physical properties including liquid crystallinity and nonlinear optical behaviour. The structural properties of the M—C=C moiety have been used in the construction of remarkable supramolecular architectures based upon squares, boxes, and other geometries. ... 

Gold(I) acetylide complexes have been prepared from alkynyllithium compounds [Eq. (22)] (63), and a dimeric complex [(PhC=C)Au(/u.-dpe)-Au(C=CPh)] [dpe = bis(diphenylphosphino)ethane] was obtained analogously. The simplest acetylide complexes are perhaps those containing only acetylide ligands. The compounds [Au(C=CPh)]x and [Au(C=C-/-Bu)]4 (1) contain cr- and 7r-bonded acetylide groups, the values of... 

Further reaction of (29 R = H) with triethylamine has given the mononuclear cyclobutenone complex (30) (52). Complexes of this type can also be obtained by cycloaddition of ketenes to the cr-acetylide (53) ... 

During the course of our studies (30-32) of the synthesis and structures of rhodium acetylide and hydrido-acetylide complexes, we developed (32) a step-wise route to rrans-bis(acetylides) of the general form mer-rra/tf-[Rh(PMe3)3(H)(C=CR) (OCR )]. Unfortunately, scrambling processes have thus far precluded the preparation of the unsymmetrically substituted complexes (R R ) in the absence of... 

The authors have previously reported33 a new convenient method of preparing transition metal-acetylide complexes of the type cis- and frans-(PR3)2M(C=CR)2 according to Eq. 10, and have shown that the complex having tri-n-butylphosphine as the ligand is air-stable and highly soluble in a variety of organic solvents. This new M-C bond formation reaction... 

Several groups have completed computational studies on the relative stabilities of osmium carbyne, carbene, and vinylidene species. DFT calculations on the relative thermodynamic stability of the possible products from the reaction of OsH3Cl(PTr3)2 with a vinyl ether CH2=CH(OR) showed that the carbyne was favored. Ab initio calculations indicate that the vinylidene complex [CpOs(=C=CHR)L]+ is more stable than the acetylide, CpOs(-C=CR)L, or acetylene, [CpOs() -HC=CR)L]+, complexes but it doesn t form from these complexes spontaneously. The unsaturated osmium center in [CpOsL]+ oxidatively adds terminal alkynes to give [CpOsH(-C=CR)L]+. Deprotonation of the metal followed by protonation of the acetylide ligand gives the vinylidene product. 

In some cases structural effects could give indications about the type of mechanism. Ziessel et al. [49, 103] have used the Pt bis-cr-acetylide spacer to construct two isomeric binuclear complexes, cis (8) and trans (9) forms, with different metal-to-... 

Organometallic complexes with two cr-acetylide ligands can act as a bidentate chelating ligand via r/ -coordination to a second metal fragment. 

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