Syntheses of dimetallamacrocycles by intramolecular oxidative couplings of dinuclear bis(1,3-butadiynyl) complexes (see abstract)
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Reactions of the chiral racemic carbonyl complex [5-C5Me5)Re(NO)(NCCH3) (CO)+BF4- and diphosphanes Ph2P(CH2)nPPh2 [2.4:1.0 mol ratio; n = 10 (a), 14 (b)] give the (bridging phosphane)dirhenium complexes [(5-C5Me5)Re(NO)(CO){- [PPh2(CH2)nPh2P]-P,P}(OC)(ON) Re(5-C5Me5)]2+2 BF4- (73-80%), which are reduced (LiAlH4) to the dimethyl complexes [(5-C5Me5)Re(NO)(CH3) {-[PPh2-(CH2)nPh2P]-P,P} (ON)(H3C)Re(5-C5Me5)] (92-96%). Reactions with HBF4OEt2/C6H5Cl, HCCCCSiMe3, and tBuOK give, via -HCC adducts (89-94%), the bis(trimethylsilyl-butadiynyl) complexes [5-C5Me5)Re(NO)(CCC CSiMe3){-[PPh2(CH2)n Ph2P]-P,P}(Me3SiCCCC)(ON)-Re (5-C5Me5)] (9a,b; 95-66%). Desilylation (wet nBu4NF) yields labile bis(butadiynyl) complexes, which are coupled [Cu(OAc)2/pyridine] to the -octatetraynediyl complexes [(5-C5Me5)Re(NO){- [PPh2(CH2)nPh2P]-P,P}{-(C1 CCCCCCC8)-C1, C8}(ON)Re(5C5Me5)] (3a,b; 10-23% from 9a,b). These represent some of the few cases of intramolecular oxidative homocouplings of terminal alkynes in metal coordination spheres. The electrochemical properties of 3a,b, which undergo two one-electron oxidations, are compared to nonmacrocyclic analogs that lack the diphosphane bridge. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).
