Rene Gutmann

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.

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).

Cyclic voltammetric study of anthraquinone-2-sulfonate in the presence of Acid Yellow 9

Abstract The electrochemical reduction of anthraquinone-2-sulfonate (AQS) has been examined in the presence of an azoic dyestuff (Acid Yellow 9, 4-amino-1,1′-azobenzene-3,4′-disulfonic acid, sodium salt) in alkaline solution. The dianion of the anthrahydroquinone-2-sulfonate (AQS2−) formed by cathodic reduction reacts with Acid Yellow 9 to regenerate AQS and yields the reduced dyestuff. The catalytic currents generated due to the chemical reaction between the AQS2− and the dyestuff have been used to estimate the rate constant of the reaction.

First regioselective protonation or selenization of a bis(bidentate) phosphine: synthesis and characterization of cis,trans,cis-1,3-bis(diphenylphosphonium)-PH,P′H′-2,4-bis(diphenylphosphino)cyclobutane-diiodide and cis,trans,cis-1,3-bis(diphenylphosphinoselenoyl)-2,4-bis(diphenylphosphino)cyclobutane

Abstract Cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) can be regioselectively protonated via oxidation with I2 and subsequent hydrolysis producing cis,trans,cis-1,3-bis(diphenylphosphonium)-PH,P′H′-2,4-bis(diphenylphosphino)cyclobutane-diiodide (dppcbH2I2). Furthermore, dppcb can be regioselectively oxidized by Se to the diselenide cis,trans,cis-1,3-bis(diphenylphosphinoselenoyl)-2,4-bis(diphenylphosphino)cyclobutane (dppcbSe2). dppcbH2I2 is the first regioselectively protonated derivative of a bis(bidentate) phosphine. In the case of dppcbSe2 the regioselective selenization of a bis(bidentate) phosphine is successful for the first time. Both dppcbH2I2 and dppcbSe2 have been fully characterized by X-ray structure analyses, NMR spectroscopy ( 77 Se { 1 H } , 31 P { 1 H } , 1 H ), FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The use of dppcbH2I2 as a precursor for the production of a heterodifunctional ligand containing phosphine and phosphinoyl moieties is discussed in view of its X-ray structure. Versatile heterodifunctional ligands like dppcbSe2 are interesting due to their possible catalytic applications.

Regioselective versus complete chalcogen transfer reactions of the bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane: full characterization of new, hemilabile ligands and their complexes with palladium(II) and platinum(II)

The bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) has been regioselectively oxidized by sulfur to the novel, hemilabile disulfide cis,trans,cis-2,3-bis(diphenylphosphinothioyl)-1,4-bis(diphenylphosphino)cyclobutane (2,3-trans-dppcbS2, I). Also the tetrachalcogenides cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphinoyl)cyclobutane (dppcbO4, II), cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphinothioyl)cyclobutane (dppcbS4, III), and cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphinoselenoyl)cyclobutane (dppcbSe4, IV) have been obtained. Regioselective selenization of the previously prepared disulfide cis,trans,cis-1,3-bis(diphenylphosphinothioyl)-2,4-bis(diphenylphosphino)cyclobutane (1,3-trans-dppcbS2) leads to the unique, mixed chalcogenide cis,trans,cis-1,3-bis(diphenylphosphinoselenoyl)-2,4-bis(diphenylphosphinothioyl)cyclobutane (trans-dppcbSe2S2, V). All of the new ligands I–V have been fully characterized by X-ray structure analyses showing folded cyclobutane rings. The coordination chemistry of the previously prepared hemilabile diselenide cis,trans,cis-1,3-bis(diphenylphosphinoselenoyl)-2,4-bis(diphenylphosphino)cyclobutane (1,3-trans-dppcbSe2), 1,3-trans-dppcbS2, I, III, and IV with PdCl2 or PtCl2 has been studied. The novel complexes [Pd2Cl4(1,3-trans-dppcbSe2-P,P′,Se,Se′)] (1), [Pt2Cl4(1,3-trans-dppcbS2-P,P′,S,S′)] (2), [PtCl2(2,3-trans-dppcbS2-P,P′)] (3), [Pt2Cl4(dppcbS4-S,S′,S″,S‴)] (4), [PtCl2(2,3-trans-dppcbSe2-P,P′)] (5), and [Pt2Cl4(2,3-trans-dppcbSe2-P,P′,Se,Se′)] (6) have been obtained. 6 has been fully characterized by an X-ray structure analysis.

Regio- and chemoselective oxidation of the bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutaneviacobalt(II) mediated dioxygen activation

The bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) has been regioselectively oxidized leading to novel, hemilabile ligands. [Co2Cl4(dppcb)] (1a) is transformed via cobalt(II) mediated dioxygen activation into [Co2Cl4(2,3-trans-dppcbO2)] (2a) in excellent yield, where 2,3-trans-dppcbO2 is cis,trans,cis-2,3-bis(diphenylphosphinoyl)-1,4-bis(diphenylphosphino)-cyclobutane. By contrast, the in situ presence of dioxygen during the synthesis of Co2Br4(dppcb)] (1b) produces both [Co2Br4(2,3-trans-dppcbO2)] (2b) and [Co2Br4(1,3-trans-dppcbO2)] (3), where 1,3-trans-dppcbO2 is cis,trans,cis-1,3-bis(diphenylphosphinoyl)-2,4-bis(diphenylphosphino)-cyclobutane. The new compounds 2a, 2b and 3 have been obtained as pure, crystalline solids and all three X-ray structure analyses have been performed showing folded cyclobutane rings. Interestingly, the corresponding reaction using [Co2I4(dppcb)] (1c) proceeds chemoselectively. Thus, [Co2I4(dppcbO3)] (4), where dppcbO3 is cis,trans,cis-1,2,3-tris(diphenylphosphinoyl)-4-diphenylphosphinocyclobutane, is formed in excellent yield and also fully characterized by an X-ray structure analysis showing two different conformations of 4. However, [Co2(NO3)4(dppcb)] (1d) shows no dioxygen activation at all. Therefore, in order to reveal the mechanism of this oxidation [Co2I4(DMF)2(dppcb)] (5) has been prepared and its X-ray structure is presented. The synthesis of [Co2I4(PMe2Ph)2(dppcb)] (6) proves that this is a common reaction pathway. Furthermore, because the product distribution of the oxidation strongly depends on the kind of halides present, the whole series Co2X4(dppcbO4)] (X = Cl, 7a; Br, 7b; I, 7c) has been prepared, where dppcbO4 is cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphinoyl)-cyclobutane, and all three X-ray structures are given, also showing folded cyclobutane rings. It seems likely that coordination of dppcb to cobalt(II) is essential to form the regio- and chemoselectively oxygenated molecules.