Positioning of transition metal centres at the upper rim of coneshaped calix[4] arenes. Filling the basket with an organometallic ruthenium unit

摘要

A series of calix[4] arenes bearing diphenylphosphino groups tethered at the upper rim have been prepared by treatment of 5,11,17,23-tetrabromo-25,26,27,28-tetrapropoxycalix[4] arene with (BuLi)-Li-t (or (BuLi)-Li-n) followed by reaction with PPh2Cl. The tetraphosphinated derivative 3 was found suitable for the formation of tetranuclear species, notably [3.(AuCl)(4)], [3.{RuCl2(p-cymene)}(4)], and [3.{PdCl(o-C6H4CH2NMe2)}(4)], all possessing an apparent C-4v-symmetry in solution. Reaction of [RuCl2(p-cymene)](2) with the diphosphines 5,17-di-X-11,23-bis(diphenylphosphino) 25,26,27,28-tetrapropoxycalix[4] arene (X=H, 1; X=Br, 4) afforded the C-2v-symmetrical dinuclear complexes [1.{RuCl2(p-cymene)}(2)] and [4.{RuC(l)2 (p-cymene)}(2)], respectively. Reaction of the non-brominated diphosphine 1 with [PdCl(o-C6H4CH2NMe2)](2) gave the complex [1.{PdCl(o-C6H4CH2NMe2)} 2]. Reaction at high dilution of [PtCl2(1,5-cyclooctadiene)] with 4 or 1 resulted in quantitative formation of the corresponding cis-chelate complexes [4.PtCl2] (12) and [1.PtCl2] (13), respectively. The trans version of 13 could also be obtained, provided that [PtCl2 (PhCN)(2)] was used as starting complex. In the solid state, the PtCl2 unit of 12 is directed towards one bromine atom, resulting in a highly unsymmetrical calixarene structure where the metal plane is nearly parallel to the calix reference plane. The NMR spectra of 12 and 13 show an apparent C-2v-symmetrical structure, suggesting a fast fan-like motion in solution of the metal plane about the P...P axis. Similar dynamics are likely to occur in the related cationic complexes [1.Rh( norbornadiene)] BF4(15) and [1.Pd(Me-allyl)]BF4 (16). As shown by variable temperature studies carried out on 12 and 16, these dynamics couple with a concomitant, restricted rotation of the two PPh2 units about their coordination axis. The latter motion is probably a result of steric interactions within the phosphorus environment, two PPh rings being in competition for occupation of the cavity entrance. Reaction of the expanded cavity 5,11,17-tribromo-23-diphenylphosphino-25,26,27,28-tetrapropoxycalix[4] arene 5 with [RuCl2(p-cymene)](2) afforded the monophosphine complex [5.RuCl2(p-cymene)]. In solution as well in the solid state, the p-cymene ligand fills the calixarene basket. [References: 34]