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(diphenylphosphino

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 (77Se{1H}, 31P{1H}, 1H), 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.