N-Alkyne complexes

From the energetically preferred n-alkyne complex there is an alternative pathway involving the hydride ligand (Figure 5). The first step is an easy (AE = 6.6 kcal.mol 1) migratory insertion of the C=C triple bond into the cis Ru-H bond to yield a a-vinyl complex, A, 10.4 kcal.mol 1 below the it-alkyne complex. This 14-electron o-vinyl complex has also a saw-horse... 

Alkenes (unsaturated hydrocarbons with double bonds) are the oldest and most studied carbon ligands, with interest in their study dating from around 1827 [3,185-189]. An important aspect is the structure of 71-alkene and similar n-alkyne complexes. Their structural data is summarized in reviews [186-189] and presented in... 

The reduction of m ,m -(isodiCp)2TiCl2 with magnesium or LiBu affords the corresponding monochloro Ti(m) derivative, while the reduction with an excess of magnesium in the presence of bis(trimethylsilyl)ethylene (btmsc) gives the Ti(n)-alkyne complex.1111... 

CpM(C0)2Co2(C0)g(u3-CPh)] (M=Fe, Ru). The interaction of ethyne with a Ptdn) surface has been modelled by reaction of ethyne with [Pt3(u3-H)(u-dppm)3) forming (140) via an intermediate n -alkyne complex. 

Cycloaromatization of enediynes by diradical pathways in the thermal-and metal-catalyzed routes allows nonfunctionalized benzene derivatives to be prepared. The aromatization of enediynes by the action of nucleophiles produces aromatic compounds retaining the respective nucleophilic residue [333, 334]. The ruthenium-catalyzed reaction gives rise to the synthesis of various functionalized benzene derivatives. Thus, adding water, alcohols, aniline, acetylacetone, pyrroles, and dimethyl malonate to acyclic and aromatic enediynes 3.711 at 100°C for 12-24 hours in the presence of TpRuPPh3(MeCN)2PF6 (10 mol%) led to the functionalized benzenes 3.712 in satisfactory yields (Scheme 3.79) [334]. This cyclization involves regioselective nucleophilic attack of enediyne 3.711 to form a, TT-vinylruthenium intermediate 3.714 which finally converts to the benzene derivative. Experiment with labeled hydrogen atoms showed that the ruthenium n-alkyne complexes 3.713 are catalytically active. 

In some instances formation of ( 0) may be avoided by employing alkyne displacement reactions. Thus (32) is formed in essentially quantitative yield by reacting L(n-CsH5)(0C)2W = CRl with the bridged alkyne complex fNi2(y-Me3SiC2SiMe3)(n-C5H5)2] (9). 

Schore, N. E. Transition Metal Alkyne Complexes Pauson-Khand Reaction. In Comprehensive Organometallic Chemistry II Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. Elsevier Oxford, 1995 Vol. 12, pp 703-739. 

The reaction of 2-formyl- and 2-acetylarylpalladium(n) bromide complexes 201 with internal alkynes and TIOTf affords indenols at room temperature, whereas cationic 2-formylarylpalladium(ll) pyridine complexes 202 do not react with alkynes at room temperature but afford indenones at 90 °C (Scheme 94). 

The isomerization, itself, originates from the a complex (B in Figure 3). However the total activation energy depends critically on the relative energy of A and B (Figure 3). An alkyne C=C triple bond binds more efficiently to a transition metal complex than a o C-H bond since the % C-C orbital is a better electron-donor and the 71 C-C orbital a better electron acceptor than the a and a C-H orbitals, respectively. However, the difference in energy between the two isomers is relatively low for a d6 metal center because four-electron repulsion between an occupied metal d orbital and the other n C-C orbital destabilizes the alkyne complex. This contributes to facilitate the transformation for the Ru11 system studied by Wakatsuki et al. 

The acetylene coordinates trans to the least o electron donor group, chlorine. Coordination of the C-H bond is a less favorable alternative to coordination of the n system. The o C-H complex is 17.1 kcal.mol 1 less stable than the rc-alkyne complex (Figure 5). From this c C-H intermediate the 1,2 shift is possible with a relatively small activation barrier (+15.5 kcaLmol 1) to yield the vinylidene complex. However this mechanism is in contradiction with the labeling experiment. 

Other possible mechanisms, corresponding to those discussed for the alkyne, have been considered. The oxidative addition pathway is excluded because all vinyl intermediates (see below) are found at high energy with respect to the n olefin complex. 

Schore NE (1991) Org React 40 1 Schore NE (1991) The Pauson-Khand reaction. In Trost BM (ed) Comprehensive organic synthesis, vol 5. Pergamon Press, Oxford, p 1037 Pauson PL (1985) Tetrahedron 41 5855 Schore NE (1995) Transition metal alkyne complexes Pauson-Khand reaction. In Abel EW, Stone EGA, Wilkinson G (eds) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford, p 703 Iwasawa N (1992) Chem Lett 473... 

The chemistry of alkyne complexes is somewhat more complicated than that of alkene complexes because of the greater possibilities for -n bonding by alkynes and the tendency of some of die complexes to act as intermediates in the formation of other organometallic compounds. 

Cross-coupling reactions 5-alkenylboron boron compounds, 9, 208 with alkenylpalladium(II) complexes, 8, 280 5-alkylboron boron, 9, 206 in alkyne C-H activations, 10, 157 5-alkynylboron compounds, 9, 212 5-allylboron compounds, 9, 212 allystannanes, 3, 840 for aryl and alkenyl ethers via copper catalysts, 10, 650 via palladium catalysts, 10, 654 5-arylboron boron compounds, 9, 208 with bis(alkoxide)titanium alkyne complexes, 4, 276 carbonyls and imines, 11, 66 in catalytic C-F activation, 1, 737, 1, 748 for C-C bond formation Cadiot-Chodkiewicz reaction, 11, 19 Hiyama reaction, 11, 23 Kumada-Tamao-Corriu reaction, 11, 20 via Migita-Kosugi-Stille reaction, 11, 12 Negishi coupling, 11, 27 overview, 11, 1-37 via Suzuki-Miyaura reaction, 11, 2 terminal alkyne reactions, 11, 15 for C-H activation, 10, 116-117 for C-N bonds via amination, 10, 706 diborons, 9, 167... 

According to reaction (a) mixed substituted platinum(0)complexes of the hitherto unknown type Ptl L1 and PtLL 2 (where L and L are phosphorus ligands) can be isolated and characterized by nmr spectroscopy. Instead of Ph3P other R3P derivatives and Ph3As can be used. Complex D is very labile. IR data give evidence for a a-coordination of the CS2ligands. With the double ylide RR N-P(S)=NR (reaction (c) ) the four-membered chelate complex E with pentavalent phosphorus of coordination number four is formed. Compound F is an example of the well characterized alkyne complexes (here with the phospha(III)azene ligand L). 

The structures of n-ethyne complexes are more diverse compared to similar olephinic structures. Important modes of ligation of alkynes to single metal atoms and clusters of two to four metal atoms are presented in Ref. 184f. Some authors divide these complexes into three types [190], where ... 

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