Several novel binuclear PdII, PtII, and PtIV complexes of trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) or cis,trans,cis-1,2,3,4- tetrakis(diphenylphosphino)cyclobutane (dppcb) have been prepared and characterized by X-ray diffraction methods, 195Pt{1H} and 31P{1H} NMRspectroscopy,FABmass spectrometry, IR spectroscopy, elemental analyses and melting points. The X-ray structure andNMRparameters of [Pt2I4(trans-dppen)2] (1) confirm that homobimetallic complexes of the type [M2L4(trans-dppen)2] (MsNi, Pd, Pt; LsCly, Iy, CNy) contain two square planar coordination units joined by two trans-dppen bridges in the solid as well as in the solution state. An analogous structure type is retained in the PtIV compound [Pt2Cl8(trans-dppen)2] (2). In contrast to the corresponding PtII complex of the new tetradentate phosphine dppcb, the X-ray structure of [Pd2Cl4(dppcb)] (3) reveals only one conformation. This can be explained by the longer Pd-P bonds compared with the Pt-P bonds and the weaker square planar stabilization energy in 3. In 3 dppcb acts as a binuclear tetraligate single-bridging ligand combining two square planar coordination centres. The reaction of Pd(CN)2 with dppcb leads to [Pd2(CN)4(dppcb)] (4). The removal of the coordinated chlorides in 3 by AgBF4 followed by subsequent treatment with NaNO2 produces [Pd2(NO2)4(dppcb)] (5). In an analogous reaction with 1,10-phenanthroline (phen) or 2,29-bipyridine (bipy), [Pd2(dppcb)- (phen)2](BF4)4 (6) and [Pd2(dppcb)(bipy)2](BF4)4 (7) are formed. The complexes 4-7 show structure types corresponding to the X-ray structure of 3. The same is true for the treatment of 3 with PMePh2 or PMe2Ph, where [Pd2(dppcb)(PMePh2)4](BF4)2Cl2 (8) and [Pd2(dppcb)(PMe2Ph)4](BF4)4 (9) are obtained. However, the X-ray structure of 8 reveals that the chlorides are coordinated in the solid state, and the crystal structure consists of trans-[Pd2Cl2(dppcb)(PMePh2)2](BF4)2 (10). The flexibility and stereochemical demands of dppcb in the compounds 3-10 and related species are discussed in view of the possible application of PdII complexes containing bidentate tertiary phosphine ligands as catalysts for the alternating copolymerization of ethene and carbon monoxide. In this respect dppcb can be regarded as a combination of two bidentate phosphines, where the cyclobutane ring corresponds to a relatively rigid ligand backbone. This produces strain in the five-membered rings of 3-10 which is released by 'envelope'-folding in the X-ray structures of 3 and 10.
Palladium(II), platinum(II), and platinum(IV) complexes containing trans-1,2-bis(diphenylphosphino)ethene or cis,trans,cis-1,2,3,4- tetrakis(diphenylphosphino)cyclobutane: complete X-ray structural characterization of binuclear compounds
Oberhauser Werner;
2000
Abstract
Several novel binuclear PdII, PtII, and PtIV complexes of trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) or cis,trans,cis-1,2,3,4- tetrakis(diphenylphosphino)cyclobutane (dppcb) have been prepared and characterized by X-ray diffraction methods, 195Pt{1H} and 31P{1H} NMRspectroscopy,FABmass spectrometry, IR spectroscopy, elemental analyses and melting points. The X-ray structure andNMRparameters of [Pt2I4(trans-dppen)2] (1) confirm that homobimetallic complexes of the type [M2L4(trans-dppen)2] (MsNi, Pd, Pt; LsCly, Iy, CNy) contain two square planar coordination units joined by two trans-dppen bridges in the solid as well as in the solution state. An analogous structure type is retained in the PtIV compound [Pt2Cl8(trans-dppen)2] (2). In contrast to the corresponding PtII complex of the new tetradentate phosphine dppcb, the X-ray structure of [Pd2Cl4(dppcb)] (3) reveals only one conformation. This can be explained by the longer Pd-P bonds compared with the Pt-P bonds and the weaker square planar stabilization energy in 3. In 3 dppcb acts as a binuclear tetraligate single-bridging ligand combining two square planar coordination centres. The reaction of Pd(CN)2 with dppcb leads to [Pd2(CN)4(dppcb)] (4). The removal of the coordinated chlorides in 3 by AgBF4 followed by subsequent treatment with NaNO2 produces [Pd2(NO2)4(dppcb)] (5). In an analogous reaction with 1,10-phenanthroline (phen) or 2,29-bipyridine (bipy), [Pd2(dppcb)- (phen)2](BF4)4 (6) and [Pd2(dppcb)(bipy)2](BF4)4 (7) are formed. The complexes 4-7 show structure types corresponding to the X-ray structure of 3. The same is true for the treatment of 3 with PMePh2 or PMe2Ph, where [Pd2(dppcb)(PMePh2)4](BF4)2Cl2 (8) and [Pd2(dppcb)(PMe2Ph)4](BF4)4 (9) are obtained. However, the X-ray structure of 8 reveals that the chlorides are coordinated in the solid state, and the crystal structure consists of trans-[Pd2Cl2(dppcb)(PMePh2)2](BF4)2 (10). The flexibility and stereochemical demands of dppcb in the compounds 3-10 and related species are discussed in view of the possible application of PdII complexes containing bidentate tertiary phosphine ligands as catalysts for the alternating copolymerization of ethene and carbon monoxide. In this respect dppcb can be regarded as a combination of two bidentate phosphines, where the cyclobutane ring corresponds to a relatively rigid ligand backbone. This produces strain in the five-membered rings of 3-10 which is released by 'envelope'-folding in the X-ray structures of 3 and 10.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
