Diphosphination of Electron Poor Alkenes

Studies of the reactions between an unsymmetrically substituted 1,1-diaminodiphosphine and electron poor alkenes revealed that, in contrast to the regioselective 1,2-addition of the P−P bond to α,β-unsaturated esters and nitriles with terminal double bonds, ethyl(vinyl)ketone reacted via 1,4-addition and α,β-unsaturated esters or ketones with internal double bonds failed to react at all, presumably owing to the deactivating influence of the alkyl groups. Reaction of 1 with maleic N-phenylimide proceeded stereoselectively under cis-addition but diesters of maleic and fumaric acid gave mixtures of diastereomeric 1,2-bisphosphines. The addition products were characterized by 31P NMR before being converted into palladium complexes that were isolated and comprehensively characterized by spectroscopic data and in most cases by X-ray diffraction studies. Monitoring the reactions of 1 with maleic and fumaric diesters by NMR revealed that both E/Z-isomerization of alkene starting materials and epimerization of stereogenic centers in 1,2-bisphosphines take place and allow isolation from the mixtures of diastereomeric ligands of complexes featuring a uniform stereochemistry of the C2 backbone

Diphosphination of Electron Poor Alkenes

Studies of the reactions between an unsymmetrically substituted 1,1-diaminodiphosphine and electron poor alkenes revealed that, in contrast to the regioselective 1,2-addition of the P−P bond to α,β-unsaturated esters and nitriles with terminal double bonds, ethyl(vinyl)ketone reacted via 1,4-addition and α,β-unsaturated esters or ketones with internal double bonds failed to react at all, presumably owing to the deactivating influence of the alkyl groups. Reaction of 1 with maleic N-phenylimide proceeded stereoselectively under cis-addition but diesters of maleic and fumaric acid gave mixtures of diastereomeric 1,2-bisphosphines. The addition products were characterized by 31P NMR before being converted into palladium complexes that were isolated and comprehensively characterized by spectroscopic data and in most cases by X-ray diffraction studies. Monitoring the reactions of 1 with maleic and fumaric diesters by NMR revealed that both E/Z-isomerization of alkene starting materials and epimerization of stereogenic centers in 1,2-bisphosphines take place and allow isolation from the mixtures of diastereomeric ligands of complexes featuring a uniform stereochemistry of the C2 backbone

A Ligand-Bridged Heterotetranuclear (Fe₂Cu₂) Redox System with Fc/Fc⁺ and Radical Ion Intermediates

The redox pair [(μ-abcp)­{Cu­(dppf)}₂]^2+/+ (abcp = 2,2′-azobis­(5-chloropyrimidine) and dppf =1,1′-bis­(diphenylphosphino)­ferrocene) has been structurally characterized to reveal the lengthening of the NN and shortening of the CN_azo bonds on reduction, each by about 0.04 Å. These and other charge forms, [(μ-abcp)­{Cu­(dppf)}₂]^<i>n</i>+ (n = 0, 3+, 4+), have been investigated spectroelectrochemically (UV–vis–near-IR, EPR) to reveal an abcp-based second reduction and a stepwise ferrocene-centered oxidation of the 2+ precursor. In contrast to the small but detectable comproportionation constant of <i>K</i>_c = 17 for the Fc/Fc⁺ mixed-valence (3+) charge state, the monocationic radical complex exhibits a very large <i>K</i>_c value of 10¹⁶

Diphosphination of Electron Poor Alkenes

Studies of the reactions between an unsymmetrically substituted 1,1-diaminodiphosphine and electron poor alkenes revealed that, in contrast to the regioselective 1,2-addition of the P−P bond to α,β-unsaturated esters and nitriles with terminal double bonds, ethyl(vinyl)ketone reacted via 1,4-addition and α,β-unsaturated esters or ketones with internal double bonds failed to react at all, presumably owing to the deactivating influence of the alkyl groups. Reaction of 1 with maleic N-phenylimide proceeded stereoselectively under cis-addition but diesters of maleic and fumaric acid gave mixtures of diastereomeric 1,2-bisphosphines. The addition products were characterized by 31P NMR before being converted into palladium complexes that were isolated and comprehensively characterized by spectroscopic data and in most cases by X-ray diffraction studies. Monitoring the reactions of 1 with maleic and fumaric diesters by NMR revealed that both E/Z-isomerization of alkene starting materials and epimerization of stereogenic centers in 1,2-bisphosphines take place and allow isolation from the mixtures of diastereomeric ligands of complexes featuring a uniform stereochemistry of the C2 backbone

New Plumbylenes and a Plumbylene Dimer with a Short Lead−Lead Separation^†^,1

The diarylplumbylene R2Pb:  (3), R = 2-tBu-4,5,6-Me3C6H, and the rearranged alkylarylplumbylene RR‘Pb:, R = 2,4,6-tBu3C6H2, R‘ = CH2C(CH3)2-3,5-tBu2C6H3, were synthesized and characterized by NMR and UV/vis spectroscopy, as well as by X-ray crystallography. Treatment of 3 with the disilylplumbylene R‘‘2Pb:, R‘‘ = Si(SiMe3)3, furnished the heteroleptic plumbylene RR‘‘Pb:  (8), which, in the solid state, forms the plumbylene dimer RR‘‘PbPbRR‘‘ (9). The X-ray structure analysis of 9 reveals a trans-bent angle of 46.5° and a Pb...Pb separation of 3.37 Å, the shortest observed so far between the lead atoms of two plumbylenes

A Ligand-Bridged Heterotetranuclear (Fe₂Cu₂) Redox System with Fc/Fc⁺ and Radical Ion Intermediates

The redox pair [(μ-abcp)­{Cu­(dppf)}₂]^2+/+ (abcp = 2,2′-azobis­(5-chloropyrimidine) and dppf =1,1′-bis­(diphenylphosphino)­ferrocene) has been structurally characterized to reveal the lengthening of the NN and shortening of the CN_azo bonds on reduction, each by about 0.04 Å. These and other charge forms, [(μ-abcp)­{Cu­(dppf)}₂]^<i>n</i>+ (n = 0, 3+, 4+), have been investigated spectroelectrochemically (UV–vis–near-IR, EPR) to reveal an abcp-based second reduction and a stepwise ferrocene-centered oxidation of the 2+ precursor. In contrast to the small but detectable comproportionation constant of <i>K</i>_c = 17 for the Fc/Fc⁺ mixed-valence (3+) charge state, the monocationic radical complex exhibits a very large <i>K</i>_c value of 10¹⁶

Spectroelectrochemistry and DFT Analysis of a New {RuNO}<i>ⁿ</i> Redox System with Multifrequency EPR Suggesting Conformational Isomerism in the {RuNO}⁷ State

The compound [Ru(NO)(bpym)(terpy)](PF6)3, bpym = 2,2‘-bipyrimidine and terpy = 2,2‘:6‘,2‘ ‘-terpyridine, with a {RuNO}6 configuration (angle Ru−N−O 175.2(4)°) was obtained from the structurally characterized precursor [Ru(NO2)(bpym)(terpy)](PF6), which shows bpym-centered reduction and metal-centered oxidation, as evident from EPR spectroscopy. The relatively labile [Ru(NO)(bpym)(terpy)]3+, which forms a structurally characterized acetonitrile substitution product [Ru(CH3CN)(bpym)(terpy)](PF6)2 upon treatment with CH3OH/CH3CN, is electrochemically reduced in three one-electron steps of which the third, leading to neutral [Ru(NO)(bpym)(terpy)], involves electrode adsorption. The first-two reduction processes cause shifts of ν(NO) from 1957 via 1665 to 1388 cm-1, implying a predominantly NO-centered electron addition. UV−vis-NIR Spectroscopy shows long-wavelength ligand-to-ligand charge transfer absorptions for [RuII(NO-I)(bpym)(terpy)]+ in the visible region, whereas the paramagnetic intermediate [Ru(NO)(bpym)(terpy)]2+ exhibits no distinct absorption maximum above 309 nm. EPR spectroscopy of the latter at 9.5, 95, and 190 GHz shows the typical invariant pattern of the {RuNO}7 configuration; however, the high-frequency measurements at 4 and 10 K reveal a splitting of the g1 and g2 components, which is tentatively attributed to conformers resulting from the bending of RuNO. DFT calculations support the assignments of oxidation states and the general interpretation of the electronic structure

Spectroelectrochemistry and DFT Analysis of a New {RuNO}<i>ⁿ</i> Redox System with Multifrequency EPR Suggesting Conformational Isomerism in the {RuNO}⁷ State

The compound [Ru(NO)(bpym)(terpy)](PF6)3, bpym = 2,2‘-bipyrimidine and terpy = 2,2‘:6‘,2‘ ‘-terpyridine, with a {RuNO}6 configuration (angle Ru−N−O 175.2(4)°) was obtained from the structurally characterized precursor [Ru(NO2)(bpym)(terpy)](PF6), which shows bpym-centered reduction and metal-centered oxidation, as evident from EPR spectroscopy. The relatively labile [Ru(NO)(bpym)(terpy)]3+, which forms a structurally characterized acetonitrile substitution product [Ru(CH3CN)(bpym)(terpy)](PF6)2 upon treatment with CH3OH/CH3CN, is electrochemically reduced in three one-electron steps of which the third, leading to neutral [Ru(NO)(bpym)(terpy)], involves electrode adsorption. The first-two reduction processes cause shifts of ν(NO) from 1957 via 1665 to 1388 cm-1, implying a predominantly NO-centered electron addition. UV−vis-NIR Spectroscopy shows long-wavelength ligand-to-ligand charge transfer absorptions for [RuII(NO-I)(bpym)(terpy)]+ in the visible region, whereas the paramagnetic intermediate [Ru(NO)(bpym)(terpy)]2+ exhibits no distinct absorption maximum above 309 nm. EPR spectroscopy of the latter at 9.5, 95, and 190 GHz shows the typical invariant pattern of the {RuNO}7 configuration; however, the high-frequency measurements at 4 and 10 K reveal a splitting of the g1 and g2 components, which is tentatively attributed to conformers resulting from the bending of RuNO. DFT calculations support the assignments of oxidation states and the general interpretation of the electronic structure

Spectroelectrochemistry and DFT Analysis of a New {RuNO}<i>ⁿ</i> Redox System with Multifrequency EPR Suggesting Conformational Isomerism in the {RuNO}⁷ State

The compound [Ru(NO)(bpym)(terpy)](PF6)3, bpym = 2,2‘-bipyrimidine and terpy = 2,2‘:6‘,2‘ ‘-terpyridine, with a {RuNO}6 configuration (angle Ru−N−O 175.2(4)°) was obtained from the structurally characterized precursor [Ru(NO2)(bpym)(terpy)](PF6), which shows bpym-centered reduction and metal-centered oxidation, as evident from EPR spectroscopy. The relatively labile [Ru(NO)(bpym)(terpy)]3+, which forms a structurally characterized acetonitrile substitution product [Ru(CH3CN)(bpym)(terpy)](PF6)2 upon treatment with CH3OH/CH3CN, is electrochemically reduced in three one-electron steps of which the third, leading to neutral [Ru(NO)(bpym)(terpy)], involves electrode adsorption. The first-two reduction processes cause shifts of ν(NO) from 1957 via 1665 to 1388 cm-1, implying a predominantly NO-centered electron addition. UV−vis-NIR Spectroscopy shows long-wavelength ligand-to-ligand charge transfer absorptions for [RuII(NO-I)(bpym)(terpy)]+ in the visible region, whereas the paramagnetic intermediate [Ru(NO)(bpym)(terpy)]2+ exhibits no distinct absorption maximum above 309 nm. EPR spectroscopy of the latter at 9.5, 95, and 190 GHz shows the typical invariant pattern of the {RuNO}7 configuration; however, the high-frequency measurements at 4 and 10 K reveal a splitting of the g1 and g2 components, which is tentatively attributed to conformers resulting from the bending of RuNO. DFT calculations support the assignments of oxidation states and the general interpretation of the electronic structure

Structures and Redox Properties of Metal Complexes of the Electron-Deficient Diphosphine Chelate Ligand <i>R</i>,<i>R</i>-QuinoxP

The air-stable chiral diphosphine chelate ligand R,R-QuinoxP (L; 2,3-bis(tert-butylmethylphosphino)quinoxaline) as developed by Imamoto et al. has been used to obtain the crystallographically characterized complexes (L)PtCl2 (1), (L)PdCl2 (2), and (L)Re(CO)3Cl (3). Coordination was found to occur via the P donor atoms, as indicated by crystal structures and NMR studies; the quinoxaline N donors do not participate in any coordination to the metals. The stereochemical arrangements observed illustrate the enantioselectivity reported for catalysis involving complexes of L. Electron acceptance by the quinoxaline heterocycle is responsible not only for the improved stability of L toward air but also for rather facile reduction of the complexes to the persistent radical anions 1•− and 3•−. In contrast, the reduction to 2•− proceeds irreversibly even at 243 K in the absence of excess chloride. EPR, UV–vis, and IR spectroelectrochemistry was used, when possible, to establish the spin location in the quinoxaline π system with rather small contributions from the metals or the phosphorus nuclei