Alkynyl complexes applications

Conjugate addititxis to a,p-unsaturated carbene complexes have not been extensively studied however, from the few reports that have appeared in the literature one can get a brief sense of the scope, limitations and special features of these reactions that may ultimately find application in synthetic organic chemistry. One of the earliest examples involves the addition of amines to alkynyl carbene complexes. The example in Scheme 19 is particularly interesting because complete control between 1,4- versus 1,2-addition can be exercised simply by proper choice of reaction temperature. The complex (119) suffers exclusive 1,2-addition with dimethylamine at -90 °C and exclusive 1,4-addition at -20 C. The 1,2-adduct (120) will further react with dimethylamine, but the 1,4-adduct (122) will not. This example demonstrates the importance of being attentive to reaction conditions when preparing amino carbene complexes, such as the alkynyl complex (120), or the alkenyl complex (76) in Scheme 11. 

Cp(CO)2Fe-C=CR (R = H, Ph, Bu, C=CH) and Cp (CO)2Fe-C=CH concluded that alkynyl-to-metal n donation is significant and destabilises the metal d levels due to filled-filled interactions, while metal-to-ligand 7i backdonation is very weak." " The same overall picture obviously applies to bis(alkynyl) complexes C=CR)2(PR3)2 of palladium and platinum. Application of... 

The NLO properties of organometallic and coordination complexes are also rich (21, 184, 279-296). Metal-alkyne complexes were first reported 1960 (297) and have recently attracted significant interest because of their potential in materials applications (2, 298). Studies of these types (299) have resulted in the development of structure-NLO response relationships for quadratic optical nonlinearities (p-value), which increase with valence electron count and ease of oxidation of metal. The amplitude is also tunable by ancillary ligand modification and substitution. Select small alkynyl complexes have been shown to exhibit p values at 1064 nm > 2600 x 10 ° esu (299). 

The use of metal alkynyl complexes, particularly with respect to the work by Humphreys and co-workers in nonlinear optical (NLO) applications, will be covered elsewhere (see Ghapter 6.09) and thus will be only briefly mentioned here with respect to the synthesis and types of alkynyl complexes reported. Emphasis has been placed... 

This synthetic protocol, although not widely applicable to various transition metals, provides a convenient route for the preparation of metal alkynyl complexes without the use of Cu(i) catalyst or strongly basic alkynylating reagents (Scheme 10.8). This metal-free method not only opens up the possibility of using a wider range of alkynyl ligands in the preparation of metal alkynyls but also eliminates possible -coordination of the catalyst to the alkynyl units. 

Zinc catalysts have shown a major increase in their possible applications. Some examples of catalysis using halide complexes, including immobilized catalytic systems, have been discussed in Section 6.8.8. Some areas such as asymmetric alkynylation of aldehydes have been recently reviewed.930... 

The coupling reaction of Fischer carbene complexes, 96, with 3-alkynyl-2-thiophene carboxaldehyde leads to the formation of thieno[2,3-c]pyranones (Scheme 25) <2001TL777, 2002JOC4177>. This reaction is applicable to the oxygenated derivatives. 

Following the Fischer procedure, alkynyl carbyne complexes trans-X(CO)4M=C—CPh 189 have been obtained in 30-60% yields by reaction of (l-alkynyl)carbene complexes la,b (M = Cr, W) with BX3 (X = Cl, Br, I). To date, (l-alkynyl)carbyne compounds have found application as catalysts as well as stochiometric reagents in organic synthesis.205c-206 Among the transformations reported thus far is the formation of a 4-amino-l-metalla-l-yne-3-ene (= enamino carbyne complex) 190 by addition of HNMe2 to compound 189 (Scheme 79).207... 

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