Solution and solid state behaviour of binuclear mercury(II) compounds containing cis,trans,cis-1,2,3,4-tetrakis-(diphenylphosphino)cyclobutane: first X-ray structural characterisation of mercury(II) complexes with two different chelating phosphines

摘要

Several novel binuclear Hg” complexes of cisjrmsxis-l .2.3.4-tetrakis(diphenylphosphino)cyclobUtane (dppcb) have been prepared and characterised by X-ray diffraction methods. N7MR spectroscopy (‘99Hg{’H}. “P{’H}, ‘H). FAB mass spectrometry. IR spectroscopy. elemental analyses and melting ~ints. The tetrahedral coordination of both the Hg” centres in the homobimetallic compounds [Hg,L4(dppcb)] (L =0 41). Br (2). CN (3). NO~ (4)), synthesised by the reaction of HgL2 with dppcb. is indicated by their solution NMR parameters and is confirmed by the X-ray structures of 1—3. Though the Fermi contact term is not always dominant in determining ‘JHg.Pt the NMR parameters are correlated to the changes in the bond lengths and angles in 1—3. A comparison is given with correlations derived from similar complexes. The reaction of 4 with 2 ,2’-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to [HgAdppcbMbip~ hj(NO3X, (5) and [HgAdppcb)(phen)j(N03)4 (6). Also, for 5 and 6 the NMR data and FAB mass spectra are in agreeuz~nt with tetrahedral Hg” centres. The treatment of 4 with monophosphines produces trans-[Hg2(N03)2(dppcb)LJ(NOz): (L = P(CHPh1 (7). P(CH2CH2CN)3 (8). PPh3 (9)). In 7—9 the typical large ‘J(Hg,P) values are observed for the mocophosphines compared with the corresponding parameters for chelating dppcb. which are reduced due to the five-membered ring formation. In the reaction of 4 with the diphosphine Ph2PCH~PPh2 (dppm) and the subsequent metathesis with LiAsF6. ,~a,u~fHg~NO3Ndppcb~rl1-dppm)j(AsF6)2 (10) is formed. The X-ray structure of 10 showing coordinated and dangling phosphorus atoms of dppmn is the first complete characterisation of a Hg” complex containing two different chelating phosphines. Though in solution the dppm ligands are involved in fast intramolecular end-over-end exchange, the solution structure of 10 corresponds to its solid state structure. which is indicated by unusual J(Hg.P) values. Catalytic amounts of Hg” convert :rans-[11g2(NO+4dppcbXfl ‘-dppm)2](N03)2 into trans-[Hg2(NO~)2(dppcb)(Ti ‘-P-dppmO),I(N03)2 (11). where dppm0 is Ph2PCH2P(O)Ph~ The X-ray structure of 11 is the first complete characterisation of a Hg” compound consisting of chelating phosphine together with phosphinoyl moieties. The solid state structure and the solution NMR parameters of 11 clearly show the presence of a dang1~g —P(O)Ph- group. The complexes 1—11 illustrate the tendency that polydentate donor ligands often geometrically and entropically restrict the number of accessible structures for Hg”. Especially. the X-ray structures of 1—3. 10, and 11 indicate the preference of Hg” for tetrahedral and trigonal pyramidal coordinations in compounds containing dppcb.