Ethynyl ligands

The hydrides 44b have been found to polymerize ethylene and react with a variety of protic reagents such as terminal alkynes and nitriles. Catalytic effects in the hydroboration of olefins have also been observed [27]. A well-defined /i-ethynyl complex of yttrium is formed by protolysis of the alkyl derivative 38b with acetylene (Eq. 18). Figure 14 shows the dimeric structure of 45b with bridging ethynyl ligands [27, 65]. 

Figure 12.3 Emission spectra of Pt(II) complex 84 (dotted line) and its PtNd2 (solid line), PtEr2 (dashed line), and PtYb2 (dash-dotted line) adducts in dichloromethane solutions at 298 K [129]. (Reprinted with permission from H.B. Xu et aL, Modulation of Pt Ln energy transfer in PtLn2 (Ln = Nd, Er, Yb) complexes with 2,2 -bipyridyl/2,2 6 2 -terpyridyl ethynyl ligands, Crystal Growth and Design, 9, 569, 2009. 2009 American Chemical Society.)...

Ni, J., Zhang, L.-Y, and Chen, Z.-N. (2009) Syntheses, characterization and sensitized lanthanide luminescence of heteronuclear Pt—Ln (Ln = Eu, Nd, Yb) complexes with 2,20-bipyridyl ethynyl ligands. Journal of Organometallic Chemistry, 694, 339. 

Fig. 1. Intermolecular interactions between ethynyl ligands of Mo2(C=CH)4(PMej)4 (I5b). Inset Intermolecular interactions in crystalline acetylene at T = 131 K 153).

One final structure in this series is the bis-TMEDA-solvated bis(phenylethynyl)magnesium species characterized as a monomer (111). ° Note the octahedral geometry of the central magnesium with two axial ethynyl ligands. This series of alkynic structures, (106)-(lil). serves to underscore the unpredictability of carbanion crystal structures. The alkynic carbanions have coordination numbers of one, two or three in these complexes. 

On the other hand, the fluxional process for [Fpf(C=CH)]BF4 gave data consistent with a 1,2-proton shift where the H atom on the ethynyl ligand... 

Coupling of the ethynyl ligand of Cp Re(NO)(PPh3)(CsCH) using Cu(OAc)2 gives Cp Re(NO)(PPh3)(-CsCCsC-)(NO)(PPh3)ReCp, the (SS,RR) and SR.RS) diasteieomers of which... 

The Gladysz group have again published widely in rhenium nitro and cyclopentadiene chemistry. The diolate compounds 10 ami 11 were prqiared from the reaction of Cp Re with NBD at > 9(fC. This is a reversible process. The coupling of an ethynyl ligand in the complex (Cp )Re(NO)(PPh3)(C CH) with Cu(OAc>2 leads to the dimeric complex. 

The interaction of phenylacetylene with (Me5C5)2Sm[CH(SiMe3)2] proceeds in a different way. In this case the bimetallic product of ethynyl ligand coupling is formed [175]. Its structure established by X-ray analysis is considered below. 

Cation diiron /t-acetylide complexes exhibit novel fluxionality. For example, the complex [Fp2 (C=C-H)]BF4 [Fp = (i/5-CsMe5)Fe(CO)2] shows equilibration of the two ethynyl carbon atoms at temperatures above — 60 °C which is accompanied by coalescence of the Fp signals at 50 °C. The proposed mechanisms (Scheme 24) involve the H atom on the ethynyl ligand moving between the two ethynyl carbon atoms with or without retention of contact. However, since the complex cannot be deprotonated by stronger bases mechanism b is excluded. For the complexes [Fp2(C=C-R)]BF4 a wiper-like oscillation of the /i-acetylide ligand is proposed. 

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