Peter Brüggeller

Luminescent dinuclear Cu(I) complexes containing rigid tetraphosphine ligands.

The synthesis and the photophysics of three dinuclear copper(I) complexes containing bis(bidentate)phosphine ligands are described. The steric constraint imposed by tetrakis(di(2-methoxyphenyl)phosphanyl)cyclobutane) (o-MeO-dppcb) in combination with 2,9-dimethyl-1,10-phenanthroline in one of the complexes leads to interesting photophysical properties. The compound shows an intense emission at room temperature in deoxygenated acetonitrile solution (Φ = 49%) and a long excited-state lifetime (13.8 μs). Interestingly, at low temperature, 77 K, the emission maximum shifts to lower energy, and the excited-state lifetime increases. This observation leads to the conclusion that a mixing between the excited triplet and singlet states is possible and that the degree of mixing and population of state strongly depends on temperature, as the energy difference is quite small. The electroluminescent properties of this compound were therefore tested in light-emitting electrochemical cells (LEECs), proving that the bright emission can also be obtained by electrically driven population of the singlet state.

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.

Schulz–Flory oligomerisation of ethylene by the binuclear nickel(II) complex Ni2Cl4[cis,trans,cis-1,2,3,4-tetrakis-(diphenylphosphino)cyclobutane]

The binuclear nickel(II) complex Ni2Cl4(cyclo-tetraphos) (cyclo-tetraphos = cis,trans,cis-1,2,3,4-tetrakis-(diphenylphosphino)cyclobutane) forms, upon activation with MAO, an effective and robust catalyst for the oligomerisation of ethylene to Schulz–Flory distributions of C4–C14 olefins with a mechanism where both chain transfer and chain propagation are first order in ethylene.

Palladium (II) and platinum (II) complexes of cis-1,2-bis(diphenylphosphino)ethene: completely planar structures due to π bonding in the case of platinum (II)

Abstract Several novel Pd(II) and Pt(II) complexes containing the dipolis ligand cis-1,2-bis(diphenylphosphino)ethene (cisdppen) have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy (195Pt{1H}, 31P{1H}), IR spectroscopy, el analyses and melting points. In contrast to the former reported and directly available compounds [PdCl2(cis-dppen)] (1) and [Pd(cis-dppen)2] (BPh4)2 (3), an intermediate complex is formed in the synthesis of [PtCl2(cis-dppen)] (2). It is shown, that this intermediate is of the type [Pt(cis-dppen)2]2+. Both 2 and [Pt(cis-dppen)2](BPh4)2 (4) are fully characterized by X-ray structure analyses: 2: monoclinic, P21/m, a = 8.507(2), b = 18.236(4) c = 11.205 (2) A , β = 105.25(3)°, R = 0.052 for 3070 observered reflections (I>3σ(I); 4 monoclinic, P21/c, a = 10.718(20), b = 17.283(3), c = 24.549(5) A , β = 99.25(3)°, R = 0.028 for 5588 observed reflections (I>3σ(I)). In 2 and 4 the Pt atoms show square-planar coordinations, where in both cases the ethene bridges are strictly coplanar with the coordination planes. This gives strong evidence of a π bonding interaction including the ethene bridges. Replacement of the chlorides in 1 and 2 by 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to the square-planar compounds [Pd(cis-dppen) (bipy)](BPh4)2 (5), [Pt(cis-dppen)(bipy)](PF6)2 (6), [Pd(cis-dppen)(phen)](BPh4)2 (7 and [Pt(cis-dppen)(phen)](BF4)2 (bd8), Similar reactions with NO2− produce produce [Pd(NO2)2(cis-dppen)] (9), [Pt(NO2)2(cis-dppen)] (10) and [PtCl(NO2)(cis-dppen)] (11). From Pd(CN)2 and cis-dppen [Pd(CN2)(cis-dppen)] (12) is formed. The stability and reactivity of complexes 1–12 are discussed with respect to the known non-planar X-ray structures of [PtCl2(dppe)], where dppe is 1,2-bis(diphenylphosphino)ethane, and [Ni(cis-dppen)2](ClO4)2.

Binuclear palladium(II), platinum(II) and platinum(IV) complexes containing 1,2-bis (diphenylphosphino)acetylene: different orientations of the diphosphine-bridges due to metal-phosphorus dπ-dπ back bonding

Abstract Several novel Pd(II), Pt(II) and Pt(IV) dimers containing 1,2-bis(diphenylphosphino)acetylene (dppa) as bridging ligand have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy ( 195 Pt{ 1 H}, 31 P{H 1 H}), IR spectroscopy, elemental analyses and melting points. The X-ray structures of the former reported complexes [Pd 2 Cl 4 (dppa) 2 ] ( 1 ) and [Pt 2 Cl 4 (dppa) 2 ] ( 2 ) are given for the first time: 1 : monoclinic, P2 1 /n, a =14.401(3), b = 12.100(2), c = 15.880(3) A , β = 91.36(3)°, Z = 2, R = 0.039 for 6432 observed reflections ( 1>3σ(1)); 2: orthorhombic , Pbcn, a = 13.995(3), b = 17.669(4), c== 21.960(4) A , Z = 4, R = 0.052 for 2332 observed reflections (1>3 σ (1)). These two X-ray structures are discussed with respect to the former given ambiguous interpretation of the X-ray structure of [PtPdCl 4 (dppa) 2 ]. Replacement of the chlorides in 1 or 2 by iodides leads to [Pd 2 I 4 (dppa) 2 ] ( 3 ) or [Pt 2 I 4 (dppa) 2 ] ( 4 ). 4 is also fully characterized by an X-ray structure analysis for the first time: 4 : monoclinic, P2 1 /c, a = 10.586(2), b = 30.526(6), c = 18.383(4) A , β = 100.09(3)°, Z = 4, R = 0.061 for 4698 observed reflections (1>3 σ (1)). The X-ray structures of 1,2 and 4 reveal different orientations of the dppa bridges due to metal-phosphorus dπ-dπ back bonding leading to different angles between the square-planar coordination units, respectively. Replacement of the chlorides in 1 by NO 2 − leads to [Pd 2 (NO 2 ) 4 (dppa) 2 ] (5), whereas in 2 only one chloride can be substituted by NO 2 − and [Pt 2 Cl 3 (NO 2 ) (dppa) 2 ] ( 6 ) is formed. A similar reaction of 2 with 2,2′-bipyridine (bipy) produces [Pt 2 Cl 2 (dppa) 2 (bipy)](BF 4 ) 2 (7). Oxidation of 2 by chlorine gives the Pt(IV) dimer [Pt 2 Cl 8 (dppa) 2 ] ( 8 ). An equimolar amount of PdCl 2 reacts with one triple bond of 2 leading to [Pt 2 PdCl 6 (dppa) 2 ] ( 9 ). an analogous manner [Pd 4 Cl 8 (dppa) 2 ] ( 10 ) is formed from 1 and two equimolar amounts of PdCl 2 . The stability and reactivity of complexes 1–10 are discussed with respect to the X-ray structures of 1,2,4 and [PtPdCl 4 (dppa) 2 ].

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.

New High-Pressure Gallium Borate Ga2B3O7(OH) with Photocatalytic Activity

The new high-pressure gallium borate Ga2B3O7(OH) was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 10.5 GPa and 700 °C. For the system Ga-B-O-H, it is only the second known compound next to Ga9B18O33(OH)15·H3B3O6·H3BO3. The crystal structure of Ga2B3O7(OH) was determined by single-crystal X-ray diffraction data collected at room temperature. Ga2B3O7(OH) crystallizes in the orthorhombic space group Cmce (Z = 8) with the lattice parameters a = 1050.7(2) pm, b = 743.6(2) pm, c = 1077.3(2) pm, and V = 0.8417(3) nm(3). Vibrational spectroscopic methods (Raman and IR) were performed to confirm the presence of the hydroxyl group. Furthermore, the band gap of Ga2B3O7(OH) was estimated via quantum-mechanical density functional theory calculations. These results led to the assumption that our gallium borate could be a suitable substance to split water photocatalytically, which was tested experimentally.

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).