Controlled scrambling reactions to polyphosphanes via bond metathesis reactions

Abstract

Triphosphanes R 0 2 PP(R)PR 0 2 (9a,c: R ¼ Py; 9b R ¼ BTz), 1,3-diphenyl-2-pyridyl-triphospholane 9d and pentaphospholanes (RP) 5 (13: R ¼ Py; 18: R ¼ BTz) are obtained in high yield of up to 98% from the reaction of dipyrazolylphosphanes RPpyr 2 (5: R ¼ Py; 6: R ¼ BTz; pyr ¼ 1,3-dimethylpyrazolyl) and the respective secondary phosphane (R 0 2 PH, R 0 ¼ Cy (9a,b), t Bu (9c); PhPH(CH 2 ) 2 PHPh (9d)). The formation of derivatives 9a-d proceeds via a condensation reaction while the formation of 13 and 18 can only be explained by a selective scrambling reaction. We realized that the reaction outcome is strongly solvent dependent as outlined by the controlled scrambling reaction pathway towards pentaphospholane 13. In our further investigations to apply these compounds as ligands we first confined ourselves to the coordination chemistry of triphosphane 9a with respect to coinage metal salts and discussed the observation of different synand anti-isomeric metal complexes based on NMR and X-ray analyses as well as quantum chemical calculations. Methylation reactions of 9a with MeOTf yield triphosphan-1-ium Cy 2 MePP(Py)PCy 2 + (10 + ) and triphosphane-1,3-diium Cy 2 MePP(Py)PMeCy 2 2+ (11 2+ ) cations as triflate salts. Salt 11[OTf] 2 reacts with pentaphospholane 13 in an unprecedented chain growth reaction to give the tetraphosphane-1,4-diium triflate salt Cy 2 MePP(Py)P(Py)PMeCy 2 2+ (19[OTf] 2 ) via a P-P/P-P bond metathesis reaction. The latter salt is unstable in solution and rearranges via a rare [1,2]-migration of the Cy 2 MeP-group followed by the elimination of the triphosph-2-en-1-ium cation [Cy 2 MePPPMeCy 2 ] + (20 + ) to yield a novel 1,4,2-diazaphospholium salt (21[OTf]). Scheme 1 Application of tripyrazolylphosphane 1 in P-P bond formation reactions; (i) 2 Cy 2 PH, -2 pyrH, CH 3 CN; (ii) 3 Cy 2 PH, -3 pyrH, and CH 3 CN; (iii) 5 PhPH(CH 2 ) 2 PHPh, 4 Ppyr 3 , -PhP(pyr)(CH 2 ) 2 -P(pyr)Ph, -10 pyrH, CH 3 CN. Scheme 7 Possible formation of 16 via P-N/P-P bond metathesis reactions.This journal is

P−P Condensation and P−N/P−P Bond Metathesis: Facile Synthesis of Cationic Tri‐ and Tetraphosphanes

“…Research Articles 3586 www.angewandte.org by diffusion of Et 2 Oi nto aC H 3 CN solution of 4b[OTf] at À30 8 8C. [21] Them olecular structures are shown in the Supporting Information, Figure S2 for 4a[OTf] and in Figure 1 for 4b [OTf].S imilar to related 1,2,3-triphospholane derivatives, [16,23] both cations show an envelope conformation of the five-membered ring in the solid state in which the phenyl and the imidazoliumyl substituents adopt an all-trans configuration. TheP ÀPb ond lengths range from 2.2156(4) to 2.2291-(4) and are comparable to other structurally related 1,2,3triphospholanes.…”

“…TheP ÀPb ond lengths range from 2.2156(4) to 2.2291-(4) and are comparable to other structurally related 1,2,3triphospholanes. [24] TheP 1-P2-P3 angles with av alue of 98.261 (16)8 8 for 4a [OTf] and 101.83(4) for 4b[OTf] are more acute compared to acyclicderivatives.The 31 PNMR spectrum of 4a[OTf] reveals at room temperature two sharp resonances of an AX 2 spin system (4a[OTf]: d(P A ) = À47.4 ppm, d(P X ) = 5.5 ppm; 1 J(P A P X ) = À219 Hz), while the resonances are broadened in case of 4b[OTf] owing to dynamic behavior attributed to the presence of two conformational isomers which are in exchange. [25,26] Ad etailed discussion is given in the Supporting Information.…”

“…[15] Larger frameworks,such as hexaphosphanes, are accessible through the concept of P À N/P À Pb ond metathesis (Scheme 1, II). [16] This concept allows for ac ross exchange of bonding partners similar to olefin metathesis [17] in the reaction of ap yrazolyl-substituted phosphane featuring aPÀNbond with adiphosphane featuring aPÀPbond. In such ar eaction, the total number of P À Na nd P À Pb onds remains constant (Scheme 1, black box).…”

“…In such ar eaction, the total number of P À Na nd P À Pb onds remains constant (Scheme 1, black box). [16] Polyphosphorus cations stabilized by imidazoliumyl substituents are very scarce,a nd we envisioned the use of our recently developed PÀN/PÀPb ond metathesis strategy for their formation. Thee xchange of one pyrazolyl substituent (pyr = 3,5-dimethylpyrazol-1-yl) in tripyrazolylphosphane…”

Coordination Chemistry and Methylation of Mixed‐Substituted Tetraphosphetanes (RP−PtBu)2 (R=Ph, Py)

“…The P−P bond lengths in the complexes remain virtually unchanged compared to the free tetraphosphetane 5 . The average P−M distances in [M 5 2 ][OTf] [2.2621 Å (Cu), 2.4100 Å (Ag) and 2.2982 Å (Au)] are comparable to those reported for other coinage metal complexes of polyphosphanes . [Cu 5 2 ] + shows a distorted tetrahedral geometry around the copper atom with a N‐Cu‐N angle of 94.55(6)° and a P‐Cu‐P angle of 127.26(2)°.…”