(Ferrocenylmethyl)phosphane (1)o xidation with hydrogen peroxide, elemental sulfur and grey selenium produced (ferrocenylmethyl)phosphane oxide 1O,s ulfide 1S and selenide 1Se,r espectively,a st he first isolable primary phosphane chalcogenides lacking stericp rotection. At elevated temperatures, compound 1O disproportionated into 1 and (ferrocenylmethyl)phosphinic acid.I nr eactions with [(h 6-mes)RuCl 2 ] 2 , 1O underwent tautomerization into ap hosphanec omplex [(h 6-mes)RuCl 2 {FcCH 2 PH(OH)-kP}],w hereas 1S and 1Se lost their P-bound chalcogen atoms, giving rise to the phosphane complex [(h 6-mes)-RuCl 2 (FcCH 2 PH 2-kP)] (Fc = ferrocenyl, mes = mesitylene). No tautomerization was observed in the reactiono f1O with B(C 6 F 5) 3 ,w hich insteadp roduced aL ewis pair FcCH 2 P(O)H 2-B(C 6 F 5) 3 .P hosphane oxide 1O added to C=O bonds of aldehydes and ketonesa nd even to cumulenes PhNCE (E = Oa nd S). However,b oth PH hydrogens were only employed in the reactions with aldehydes and cyanates. Scheme1.Synthesis of P-chalcogenides 1E.
This contribution reports the synthesis of two phosphinoferrocene ligands desymmetrized by an inserted methylene spacer, viz., a bis-phosphine combining primary and tertiary phosphine moieties in its structure, Ph2PfcCH2PH2 (2), and a structurally unique, stable phosphine-primary phosphine oxide Ph2PfcCH2P(O)H2 (7; fc = ferrocene-1,1′-diyl). Compounds 2 and 7, together with 1,1′-bis(diphenylphosphino)ferrocene (dppf), the bis-tertiary phosphine Ph2PfcCH2PPh2, and the adduct Ph2P(BH3)fcCH2PH2 (6), were studied as ligands in Ru(II) complexes bearing auxiliary η6-arene ligands and both free ligands and the isolated complexes were structurally authenticated, using spectroscopic methods and X-ray crystallography, and further investigated by cyclic voltammetry. The results suggest that distinct donor moieties in the unsymmetric ligands differentiate the otherwise identical coordinated metal centers and that the phosphine moiety in phosphine-phosphine oxide ligand 7 is preferably coordinated to Ru(II), before the phosphine oxide group, which must tautomerize into the hydroxyphosphine form prior to coordination.
A boraguanidinato-stabilized germylene, [(i-Pr)NB(N-2,6-MeCH)]Ge, reacts with alkynes RC[triple bond, length as m-dash]CR selectively in a 2 : 1 molar ratio to afford 3,4-R,R'-1,2-digermacyclobut-3-enes 1a-e as the products of formal [2 + 2 + 2] cyclization [R/R' = Me/Me (1a), Ph/Ph (1b), Ph/H (1c), t-Bu/H (1d) and Cy/H (1e)]. Ferrocenyl-substituted alkynes react similarly, yielding the corresponding ferrocenylated 3,4-R,R'-1,2-digermacyclobut-3-enes 2a-d [where R/R' = Fc/H (2a), Fc/Me (2b), Fc/Ph (2c), and Fc/Fc (2d); Fc = ferrocenyl]. By contrast, only one of the triple bonds available in conjugated diynes RC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CR is activated with the germylene, while the second one remains intact even in the presence of an excess of the germylene. The exclusive formation of 3,4-R,(C[triple bond, length as m-dash]CR)-1,2-digermacyclobut-3-enes 3a-c [R = Ph (3a), t-Bu(3b), and Fc (3c)] was ascribed to a steric repulsion around the second triple bond. On the other hand, the reaction of the germylene with more flexible dialkyne fc(C[triple bond, length as m-dash]CPh) (fc = ferrocene-1,1'-diyl) proceeded in the expected manner, producing compound 4, where both triple bonds are transformed into 1,2-digermacyclobut-3-ene rings by reaction with four equivalents of the germylene. All compounds were characterized by multinuclear NMR spectroscopy, Raman and IR spectroscopy, and in the case of 1a-c, 2a, 2c, 3a, 3b and 4, also by single-crystal X-ray diffraction analysis. The ferrocenyl substituted compounds were studied by cyclic voltammetry (CV). Finally, the plausible reaction pathway was studied for a model reaction of [(i-Pr)NB(N-2,6-MeCH)]Ge with MeC[triple bond, length as m-dash]CMe using DFT computations.
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