Capping calixarenes with metallodiphosphine fragments: towards intracavity reactions

The co-ordinative properties of four disubstituted 5,11,17,23-tetra-tert-butyl-25,27-di-RCH 2 O-26,28- bis(diphenylphosphinomethoxy)calix[4]arenes [R = C(O)NEt 2 L 1 , C(O)OEt L 2 , (R)-C(O)NHCH(Me)Ph L 3 or CH 2 OMe L 4 ] have been investigated. Compound L 1 reacted with [Au(thf)(SC 4 H 8 )]BF 4 (thf = tetrahydrofuran, SC 4 H 8 = tetrahydrothiophene) and AgBF 4 to yield the chelate complexes [AuL 1 ]BF 4 1 and [AgL 1 ]BF 4 2, respectively. Reaction of L 1 with trans-[PtH(Cl)(PPh 3 ) 2 ] resulted in quantitative formation of trans-[PtH(Cl)L 1 ] 3 in which the platinum hydrogen bond is partially encapsulated within the calixarene cavity. The structurally related cationic complexes [PtH(PPh 3 )L i ]BF 4 (L i = L 1 4, L 3 5 or L 4 6), having a PPh 3 ligand trans to the hydrido ligand, were obtained in high yield by treating trans-[PtH(thf)(PPh 3 ) 2 ]BF 4 with diphosphine L i . Abstraction of the chloride ion from 3 with AgBF 4 gave [PtH(L 1 )]BF 4 7, a complex in which the calixarene behaves as a tridentate P 2 O amide ligand and in which the metal plane caps one end of the calixarene tunnel. Reaction of 7 with PPh 3 resulted in substitution of the co-ordinated amide to form 4, while reaction with 4,4′-bipyridine gave the binuclear complex [(L 1 )HPt(4,4′-bipy)PtH(L 1 )][BF 4 ] 2 8. Reaction of trans-[PtH(Cl)(PPh 3 ) 2 ] with L i resulted in a mixture of complexes of general formula [PtH(PPh 3 )L i ]Cl (type A) and [PtH(Cl)L i ] (type B). The A∶B ratio depends on the co-ordinating ability of the R groups, since these act as internal solvent molecules in promoting PPh 3 substitution. For R groups containing strong donors, e.g. as in L 1 and L 2 , complexes of type B are favoured; with L 4 the reaction leads selectively to [PtH(PPh 3 )L 4 ]Cl, no B-type complex being formed. In at least one case (L 3 ) it was shown that complexes of type A may be converted into the B type. Reaction of 7 with dimethyl acetylenedicarboxylate gave the insertion product trans-P,P′-[Pt(MeO 2 CCCHCO 2 Me)L 1 ]BF 4 where the two amides compete for co-ordination. Complex 7 reacted instantaneously with tetracyanoethylene (tcne) to yield the platinum(0) complex [Pt(tcne)L 1 ] for which NMR spectra suggest fast flipping of the co-ordination plane between amides. In contrast to [Pt(MeO 2 CCCHCO 2 Me)L 1 ]BF 4 , strong tridentate P 2 O co-ordination abounds in the rhodium carbonyl complexes [Rh(CO)L i ]BF 4 (L i = L 1 or L 3 ) obtained from [Rh(CO) 2 (thf) 2 ]BF 4 and the corresponding diphosphines.