Rainer Haid

Synthesis, platinum(II) complexes and structural aspects of the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane

Abstract Several novel dimers of the composition [M 2 Cl 4 ( trans -dppen) 2 ] (M=Ni ( 1 ), Pd ( 2 ), Pt ( 3 )) containing trans -1,2-bis(diphenylphosphino)ethene ( trans -dppen) have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy ( 195 Pt{ 1 H}, 31 P{ 1 H}), elemental analyses, and melting points. The intramolecular [2+2] photocycloaddition of the two diphosphine-bridges in 3 produces [Pt 2 Cl 4 (dppcb)] ( 4 ), where dppcb is the new tetradentate phosphine cis,trans,cis -1,2,3,4-tetrakis(diphenylphosphino)cyclobutane. Neither 1 nor the free diphosphine trans -dppen shows this reaction. In the case of 2 the photocycloaddition is slower than in 3 . This difference can be explained by the shorter distance between the two aliphatic double bonds in 3 than in 2 , but also different transition probabilities within ground and excited states of the used metals could be involved. Furthermore, variable-temperature 31 P{ 1 H} NMR spectroscopy of 2 or 3 reveals a negative activation entropy of 2 for the [2+2] photocycloaddition, but a positive of 3 . The removal of chloride from 4 by precipitating AgCl with AgBF 4 , and subsequent treatment with 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to [Pt 2 (dppcb)(bipy) 2 ](BF 4 ) 4 ( 5 ) and [Pt 2 (dppcb)(phen) 2 ](BF 4 ) 4 ( 6 ), respectively. In an analogous reaction of 4 with PMe 2 Ph or PMePh 2 , [Pt 2 (dppcb)(PMe 2 Ph) 4 ](BF 4 ) 4 ( 7 ) and [Pt 2 (dppcb)(PMePh 2 ) 4 ](BF 4 ) 4 ( 8 ) are formed. Complexes 1 – 8 show square–planar coordinations, where the compounds 4 – 8 have also been characterized by the above mentioned methods together with fast atom bombardment mass spectrometry ( 7 , 8 ). The crystal structure of 4 reveals two conformations, which arise from an energetic competition between the sterical demands of dppcb and an ideal square–planar environment of Pt(II). The free tetraphosphine dppcb can be obtained easily from 4 by treatment with NaCN. It has been characterized fully by the above methods including 13 C{ 1 H} and 1 H NMR spectroscopy. The X-ray structure analysis shows the pure MMMP-enantiomer in the solid crystal, which is therefore optically active. This chirality is induced by a conformation of dppcb, where all four PPh 2 groups are non-equivalent. Variable-temperature 31 P{ 1 H} NMR spectroscopy of dppcb confirms this explanation, since the single signal at room temperature is split into two doublets at 183 K. The goal of this article is to demonstrate the facile production of a new tetradentate phosphine from a diphosphine precursor via Pt(II) used as a template.

Nickel(II), palladium(II), platinum(II) and platinum(IV) complexes of cis-1,2-bis(diphenylphosphino) ethene and nitrogen-containing heterocycles or sulfur ligands

Several novel Ni(II), Pd(II), Pt(II) and Pt(IV) complexes containing the diphos ligand cis -1,2-bis(diphenylphosphino)ethene ( cis -dppen) have been prepared and characterized by X-ray diffraction methods. NMR spectroscopy ( 195 Pt{ 1 H}, 31 P{ 1 H, 13 C{ 1 H}, 1 H), fast atom bombardment mass spectrometry, IR spectroscopy, elemental analyses, and melting points. In the case of [PtCl 2 ( cis -dppen)] (1) a second crystal modification was found and definitely characterized by an X-ray structure analysis: monoclinic. P 2 1 / n , Z = 4, a = 8.312(1), b = 14.578(2), c = 19.868(4) A, β = 91.27(1)°, R = 0.028 for 3862 observed reflections( I > 3 σ ( I )). In contrast to the former reported X-ray structure of the other modification of 1 , which shows a complete coplanarity of the coordination plane and the ethene bridge, this coplanarity is slightly disturbed by a crystal packing effect in the second modification of 1 . Nevertheless, both conformations are dominated by a π bonding interaction. Furthermore, the X-ray structures of the recently prepared complexes [Pt( cis -dppen)(bipy)](PF 6 ) 2 ( 2 ) and [Pt( cis -dppen)(phen)](BF 4 ) 2 ( 3 ), where bipy and phen are 2,2′-bipyridine and 1,10-phenanthroline, respectively, are given for the first time: 2 : monoclinic, P 2 1 / c , Z = 4, a = 12.649(3), b = 26.114(5), c = 14.665(3) A, β = 111.62(3)°, R = 0.057 for 4260 observed reflections ( I > 3 σ ( I )); 3 : monoclinic, P 2 1 , Z = 2, a = 8.779(2), b = 17.297(3), c = 13.059(3) A, β = 93.79(3)°, R = 0.045 for 3589 observed reflections ( I > 3 σ ( I )). These two X-ray structures are the first examples of square-planar structures of Pt(II) complexes containing bipy or phen together with phosphines. The different conformations of 2 and 3 are of interest with respect to the known differences between bipy and phen in photoactivation processes. The reaction of 1 with an equimolar amount of anhydrous Na 2 S leads to the dimer [Pt 2 (μ 27 S) 2 ( cis -dppen) 2 ] ( 4 ). A similar treatment of 1 with the phosphoniodithioformate S 2 CPCy 3 , where Cy is cyclohexyl, produces the dimer [Pt 2 (μ 2 -S)(μ 2 -S 2 CPCy 3 ) ( cis -dppen) 2 ] (BF 4 ) 2 ( 5 ). However, the reactions of [MCl 2 ( cis -dppen)] (M=Ni, Pd) with anhydrous Na 2 S give the trinuclear complexes [M 3 (μ 3 -S) 2 ( cis -dppen) 3 ]X 2 (M=Ni, X − =PF 6 ( 6 ); M=Pd, X − =BF 4 ( 7 )). In the case of 1 Na 2 S · 9H 2 O is needed to produce the corresponding Pt(II) complex [Pt 3 (μ 3 -S) 2 ( cis -dppen) 3 ] Cl 2 ( 8 ). Interestingly, treatment of [NiCl 2 ( cis -dppen)] with S 2 CPCy 3 leads to the unexpected mononuclear compound [Ni(CS 2 ) 4 ( cis -dppen)] (BF 4 ) 2 ( 9 ). Oxidation of [Pt( cis -dppen) 2 ]Cl 2 by chlorine gives the mononuclear complex [PtCl 2 ( cis -dppen) 2 ]Cl 2 ( 10 ). The common feature of the compounds 1–10 is the presence of cis -dppen as a chelating ligand. The goal of this article is to reveal possible π bonding interactions due to the unsaturated nature of this diphos ligand.

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

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} NMR spectroscopy, FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The X-ray structure and NMR parameters of [Pt2I4(trans-dppen)2] (1) confirm that homobimetallic complexes of the type [M2L4(trans-dppen)2] (M=Ni, Pd, Pt; L=Cl−, I−, CN−) 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 2,2′-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.

Nickel(II), palladium(II), and platinum(II) complexes containing cis- or trans-1,2-bis(diphenylphosphino)ethene: isomorphous crystal structures in the cyanide case

Abstract Mono- and binuclear NiII, PdII, and PtII complexes of cis- or trans-1,2-bis(diphenylphosphino)ethene (cis- or trans-dppen) have been prepared and characterized by X-ray diffraction methods, 19;Pt 1H and 31P 1H NMR spectroscopy, FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The X-ray structures of some rare examples of cis-dicyanide complexes of the type [M(CN)2(cis-dppen)] (M Ni (1), M Pd (2), M Pt (3)) are given for the first time. All three crystal lattices are isomorphous and allow comparison of the radii of Ni, Pd, and Pt atoms. In 1–3 the coordination is square planar. In all cases the ethene bridges are nearly coplanar with the coordination planes, which can be explained by π-bonding interactions. Due to the isomorphous crystal lattices, 1–3 show analogous shortest intermolecular repulsive C–H···M contact approaches leading to small deviations from coplanarity. The removal of one coordinated chloride in [NiCl2(cis-dppen)] by AgBF4 followed by subsequent treatment with bis(diphenylphosphino)amine, NH(PPh2)2 (dppam), leads to the novel complex [NiCl(cis-dppen) (dppam)](BF4) (4). However, the analogous abstraction of both chlorides in [MCl2(cis-dppen)] (M Pd, Pt) and reaction with dppam produces [M(cis-dppen)(dppam)](BF4)2 (M Pd (5), M Pt (6)). In the case of trans-dppen, the reaction with Pd(CN)2 leads to another novel cis-dicyanide complex of the type [Pd2(CN)4(μ-trans-dppen)2] (7). Substitution of chloride in [Pt2Cl4(μ-trans-dppen)2] by cyanide leads to the analogous PtII compound [Pt2(CN)4(μ-trans-dppen)2] (8). It is believed, that the unsaturated nature of cis- or trans-dppen leading to π-bonding interactions with the metal-ligand bonds, is responsible for the unusual stability of cis-dicyanide complexes. For dppam the presence of electronic delocalization is well-known. These effects are discussed in view of the X-ray structures of 1–3 and related compounds.

First true square-planar Hg(II) compound: synthesis and full characterization of trans-[Hg{Ph2PNP(O)Ph2-P,O}2]

Abstract The reaction of Hg(O3SCF3)2 with bis(diphenylphosphino)amine, Ph2PNHPPh2 (dppam), produces the novel, rare face-to-face complex [Hg2(O3SCF3)4(dppam)2] (1). Treatment of 1 with Na2N2O3 leads to trans-[Hg{Ph2PNP(O)Ph2-P,O}2] (2) via regioselective oxidation and simultaneous deprotonation of dppam. 2 is the first true square-planar Hg(II) compound. In 2 the coordination plane and the five-membered rings of the HgNOP2 moieties are completely coplanar indicating strong π-bonding interactions. Both 1 and 2 have been fully characterized by X-ray structure analyses, NMR spectroscopy ( 199 Hg { 1 H }, 31 P { 1 H }, 13 C { 1 H }, 1 H ) , ESI and FAB mass spectrometry, IR spectroscopy, elemental analyses, and melting points. Since in Hg(II) compounds relativistic effects favour linear coordination and Hg(II) donor atom preferences play a significant role, the Hg–P bond length of 2.4042(7) A in 2 is short, whereas the Hg–O bond length of 2.7138(15) A is long. In view of the X-ray structures of 1 and 2, it is shown that the delocalized charge in [Ph2PNP(O)Ph2]− is responsible for the achievement of the square-planar coordination in a Hg(II) compound. A similar π-bonding effect has been observed in several square-planar complexes of Pt(II), Pd(II), and Ni(II) containing cis-1,2-bis(diphenylphosphino)ethene (cis-dppen).

Structural differences in nickel(II) and palladium(II) complexes containing cis-1,2-bis(diphenylphosphino)ethene or 1,2-bis(diphenylphosphino)ethane

Abstract Monometallic NiII and PdII complexes of cis-1,2-bis(diphenylphosphino)ethene (cis-dppen) or 1,2-bis(diphenylphosphino)ethane (dppe) have been prepared and characterized by X-ray diffraction methods, 31P 1H NMR spectroscopy, FAB mass spectrometry, elemental analyses and melting points. The X-ray structure of [NiCl2(cis-dppen)] (1) is given for the first time. In 1 the mean deviation of the nickel, the phosphorus and the chlorine atoms from a least-squares plane through these atoms is only 0.025 A. The ethene bridge is nearly coplanar with this plane, which can be explained by a π-bonding interaction. It is shown that the small deviation from coplanarity are caused by a crystal packing effect. The reaction of Ni(CN)2 with cis-dppen leads to the novel compound [Ni(CN)2(cis-dppen)] (2). The removal of chloride in 1 by AgBF4 followed by the reaction with 1,10-phenanthroline (phen) leads to the novel octahedral NiII complex [Ni(cis-dppen)(phen)2](BF4)2 (3). In an analogous manner 2,2′-bipyridine (bipy) produces [Ni(cis-dppen)(bipy)2](BF4)2 (4). The reaction of trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) with PdCl2 and subsequent treatment with LiI leads to the unexpected product [PdI2(dppe)] (5). Compound 5 is also fully characterized by an X-ray structure analysis for the first time. The palladium, phosphorus and iodine atoms show a mean deviation of only 0.017 A from a least-squares plane through these atoms. However, the PdP2C2 chelate ring has a twist conformation, where one carbon atom of the aliphatic chain of dppe lies −0.420 A to one side, and the second carbon atom 0.318 A to the other side of the coordination plane. In 5 the PPdP chelate angle of 85.59(5)° is significantly smaller than the corresponding PNiP angle of 87.79(4)° in 1. Furthermore, the X-ray structure of the recently reported complex [Pd(cis-dppen)2](BPh4)2 (6) is given. The palladium atom is located on a centre of symmetry leading to the complete planarity of the coordination plane due to crystallographic constraints. However, the two carbon atoms of the ethene bridge of cis-dppen lie 0.547 and 0.532 A, respectively, to one side of the coordination plane. Compound 6 significantly shows the smallest PMP chelate angle of 84.78(3)° compared with the corresponding values in 1 and 5. A comparison of the X-ray structures of 1,5 and 6 with several known X-ray structures of NiII and PdII complexes containing cis-dppen or dppe is given. Differences in the chelate angles and coplanar parts of these structures are discussed with respect to the observed reactivities of compounds 1–6.

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

Abstract Several novel binuclear Hg II 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 ( 199 Hg{ 1 H}, 31 P{ 1 H}, 1 H), FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The tetrahedral coordination of both the Hg II centres in the homobimetallic compounds [Hg 2 L 4 (dppcb)] (L=Cl − ( 1 ), Br − ( 2 ), CN − ( 3 ), NO 3 − ( 4 )), synthesised by the reaction of HgL 2 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 1 J (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 [Hg 2 (dppcb)(bipy) 2 ](NO 3 ) 4 ( 5 ) and [Hg 2 (dppcb)(phen) 2 ](NO 3 ) 4 ( 6 ). Also, for 5 and 6 the NMR data and FAB mass spectra are in agreement with tetrahedral Hg II centres. The treatment of 4 with monophosphines produces trans -[Hg 2 (NO 3 ) 2 (dppcb)L′ 2 ](NO 3 ) 2 (L′=P(CH 2 Ph) 3 ( 7 ), P(CH 2 CH 2 CN) 3 ( 8 ), PPh 3 ( 9 )). In 7 – 9 the typical large 1 J (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 Ph 2 PCH 2 PPh 2 (dppm) and the subsequent metathesis with LiAsF 6 , trans -[Hg 2 (NO 3 ) 2 (dppcb)(η 1 -dppm) 2 ](AsF 6 ) 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 Hg II 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 1 J (Hg,P) values. Catalytic amounts of Hg II convert trans -[Hg 2 (NO 3 ) 2 (dppcb)(η 1 -dppm) 2 ](NO 3 ) 2 into trans -[Hg 2 (NO 3 ) 2 (dppcb)(η 1 -P-dppmO) 2 ](NO 3 ) 2 ( 11 ), where dppmO is Ph 2 PCH 2 P(O)Ph 2 . The X-ray structure of 11 is the first complete characterisation of a Hg II 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)Ph 2 group. The complexes 1 – 11 illustrate the tendency that polydentate donor ligands often geometrically and entropically restrict the number of accessible structures for Hg II . Especially, the X-ray structures of 1 – 3 , 10 , and 11 indicate the preference of Hg II for tetrahedral and trigonal pyramidal coordinations in compounds containing dppcb.

First heterodifunctional ligand derived from a tetradentate phosphine: synthesis and characterization of cis,trans,cis-1,3-bis(diphenylphosphino)-2,4-bis(diphenylphosphinothioyl)cyclobutane and its complex with PdCl2

Abstract Cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) can be selectively oxidized by S in toluene to the disulfide cis,trans,cis-1,3-bis(diphenylphosphino)-2,4-bis(diphenylphosphinothioyl)cyclobutane (dppcbS2). DppcbS2 is the first heterodifunctional ligand derived from a tetradentate phosphine obtained with good yield and high purity. It reacts with two equivalents of PdCl2 producing [Pd2Cl4(dppcbS2)] (1). Both dppcbS2 and 1 have been fully characterized by X-ray structure analyses, NMR spectroscopy ( 31 P{ 1 H}, 13 C{ 1 H}, 1 H), FAB mass spectrometry, elemental analyses and melting points. The possible catalytic applications of the versatile heterodifunctional ligand dppcbS2 are discussed in view of the two X-ray structures of dppcbS2 and 1.

New structurally rigid palladium catalysts for the alternating copolymerization of carbon monoxide and ethene

Decreasing the flexibility of the Ph2PCH2CH2PPh2 (dppe) backbone by making the central carbon atoms part of a cyclobutane ring leads to the formation of Pd(II) catalysts for CO/ethene copolymerization that are more efficient than those of dppe by a factor of ten.

Structural impact of cis-1,2-bis(diphenylphosphino)ethene on the first hexanuclear palladium(II)-silver(I) complex with triply-bridging sulfide ligands

Abstract The removal of chloride from [PdCl2(cis-dppen)] (1), where cis-dppen is cis-1,2-bis(diphenylphosphino)ethene, by precipitating AgCl with AgBF4, and subsequent treatment with the phosphoniodithioformate S2CPCy3, where Cy is cyclohexyl, produces the first hexanuclear palladium(II)-silver(I) complex with triply-bridging sulfide ligands of the composition [Ag2Pd4(μ3-S)4(cis-dppen)4](BF4)2 2. 2 has been fully characterized by an X-ray structure analysis, NMR spectroscopy, FAB mass spectrometry, elemental analysis and melting point. Due to π bonding interactions cis-dppen exerts a structural impact on 2 not observed in a series of related compounds.