Cyclobutadiene complexes platinum

Complexes of platinum with tetrahapto ( j4) cyclobutadiene ligands can be prepared examples are shown in equations (288) and (289).871,872. ... 

Tetraphenylcyclobutadienepalladium and -nickel complexes and tetra-methylcyclobutadienenickel chloride react readily with nucleophilic reagents to give 7r-cyclobutenyl complexes 12, 30, 31, 65, 91), a reaction reminiscent of those described by Chatt et al. for diene-palladium and diene-platinum halide complexes (Section VI, F). Non-halogen-containing cyclobutadiene complexes, however, appear inert under similar conditions so that this reaction is very dependent on the other ligands present. Some similarity between cyclobutadiene-metal and diene-metal complexes appears to exist but how far the parallel can be drawn remains to be seen. The reactions are fully discussed in Section VI. 

The formal 2 -I- 2-cycloaddition reaction of platinum(ll) acetilides (14) with TCNE and TCNQ initially produced 7,7,8,8-tetracyano-p-quinodimethane cyclobuta-1, 3-dienes that undergo retroelectrocyclization to produce feis-cycloadducts (15, 16). In all examples investigated, the triple bond adjacent to the platinum atom did not react with the TCNE or the TCNQ (Scheme 5). The 2-I-2-cycloaddition of substituted cyclobutadiene-AlCl3 complexes (18) with methyl phenylpropynoate (17) produced Dewar benzene intermediates (19) that readily converted to 1,2,3,4-tetramethyl- and 1,2,3,4-tetraethyl-fluorenes (20) (Scheme 6). The first rhodium-catalysed inter-molecular 2-1-2-cycloaddition of terminal alkynes with e-deflcient alkenes yielded substituted cyclobutenes in high yields (99%) and complete regioselectivity. An 8-quinolinolatorhodium/phosphine catalyst (21) was employed in this reaction. ... 

Instances in which cyclobutadiene complexes are the major products from the reactions of acetylene complexes with additional alkyne are uncommon. These generally have been found to be significant products with sterically hindered alkynes and with palladium and platinum metals. For example, phenyl tert-butyl acetylene was converted to the corresponding cyclobutadiene complex (one isomer) upon treatment with (PhCN)2 PdCl2 (Hos-okawa and Moritani, 1969) [Eq. (71)]. With sterically less demanding tolane,... 

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