Several novel binuclear HgII complexes of cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) have been prepared and characterised by X-ray diffraction methods, NMR spectroscopy (199Hg{1H}, 31P{1H}, 1H), FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The tetrahedral coordination of both the HgII centres in the homobimetallic compounds [Hg2L4(dppcb)] (L=Cl- (1), Br- (2), CN- (3), NO3 - (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 1J(Hg,P), 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 [Hg2(dppcb)(bipy)2](NO3)4 (5) and [Hg2(dppcb)(phen)2](NO3)4 (6). Also, for 5 and 6 the NMR data and FAB mass spectra are in agreement with tetrahedral HgII centres. The treatment of 4 with monophosphines produces trans-[Hg2(NO3)2(dppcb)L2](NO3)2 (L=P(CH2Ph)3 (7), P(CH2CH2CN)3 (8), PPh3 (9)). In 7-9 the typical large 1J(Hg,P) values are observed for the monophosphines 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 Ph2PCH2PPh2 (dppm) and the subsequent metathesis with LiAsF6, trans-[Hg2(NO3)2(dppcb)(1-dppm)2](AsF6)2 (10) is formed. The X-ray structure of 10 showing coordinated and dangling phosphorus atoms of dppm is the first complete characterisation of a HgII 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 1J(Hg,P) values. Catalytic amounts of HgII convert trans-[Hg2(NO3)2(dppcb)(1-dppm)2](NO3)2 into trans-[Hg2(NO3)2(dppcb)(1-PdppmO) 2](NO3)2 (11), where dppmO is Ph2PCH2P(O)Ph2. The X-ray structure of 11 is the first complete characterisation of a HgII 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 dangling P(O)Ph2 group. The complexes 1-11 illustrate the tendency that polydentate donor ligands often geometrically and entropically restrict the number of accessible structures for HgII. Especially, the X-ray structures of 1-3, 10, and 11 indicate the preference of HgII for tetrahedral and trigonal pyramidal coordinations in compounds containing dppcb.
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
Oberhauser Werner;
2001
Abstract
Several novel binuclear HgII complexes of cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) have been prepared and characterised by X-ray diffraction methods, NMR spectroscopy (199Hg{1H}, 31P{1H}, 1H), FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The tetrahedral coordination of both the HgII centres in the homobimetallic compounds [Hg2L4(dppcb)] (L=Cl- (1), Br- (2), CN- (3), NO3 - (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 1J(Hg,P), 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 [Hg2(dppcb)(bipy)2](NO3)4 (5) and [Hg2(dppcb)(phen)2](NO3)4 (6). Also, for 5 and 6 the NMR data and FAB mass spectra are in agreement with tetrahedral HgII centres. The treatment of 4 with monophosphines produces trans-[Hg2(NO3)2(dppcb)L2](NO3)2 (L=P(CH2Ph)3 (7), P(CH2CH2CN)3 (8), PPh3 (9)). In 7-9 the typical large 1J(Hg,P) values are observed for the monophosphines 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 Ph2PCH2PPh2 (dppm) and the subsequent metathesis with LiAsF6, trans-[Hg2(NO3)2(dppcb)(1-dppm)2](AsF6)2 (10) is formed. The X-ray structure of 10 showing coordinated and dangling phosphorus atoms of dppm is the first complete characterisation of a HgII 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 1J(Hg,P) values. Catalytic amounts of HgII convert trans-[Hg2(NO3)2(dppcb)(1-dppm)2](NO3)2 into trans-[Hg2(NO3)2(dppcb)(1-PdppmO) 2](NO3)2 (11), where dppmO is Ph2PCH2P(O)Ph2. The X-ray structure of 11 is the first complete characterisation of a HgII 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 dangling P(O)Ph2 group. The complexes 1-11 illustrate the tendency that polydentate donor ligands often geometrically and entropically restrict the number of accessible structures for HgII. Especially, the X-ray structures of 1-3, 10, and 11 indicate the preference of HgII for tetrahedral and trigonal pyramidal coordinations in compounds containing dppcb.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
