Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies.
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abstract
The silylated hexatriynyl complex trans-(C6 F5 )(p-tol3 P)2 Pt(CC)3 SiEt3 (PtC6 TES) is converted insitu to PtC6 H (wet n-Bu4 N+ F- , THF) and cross coupled with the diyne H(CC)2 SiEt3 (HC4 TES; CuCl/TMEDA, O2 ) to give PtC10 TES (71%). This sequence is repeated twice to afford PtC14 TES (65%) and then PtC18 TES (27%). An analogous series of reactions starting with PtC8 TES gives PtC12 TES (60%), then PtC16 TES (43%), and then PtC20 TES (17%). Similar cross couplings with H(CC)2 Si(i-Pr)3 (HC4 TIPS) give PtC12 TIPS (68%), PtC14 TIPS (68%), and PtC16 TIPS (34%). The trialkylsilyl species (up to PtC18 TES) are converted to 3+2 "click" cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C6 F5 )(p-tol3 P)2 Pt(CC)n-1 C=CHN(CH2 C6 H5 )N=N (29-92% after workups). The most general procedure involves generating the terminal polyynes PtCx H (wet n-Bu4 N+ F- , THF) in the presence of benzyl azide in DMF and aqueous CuSO4 /ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC20 TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.
