Phosphonium Salts of 1,8-Bis(diphenylphosphino)naphthalene: Molecular Structures and NMR-spectroscopic Studies

Abstract

A representative series of diphosphine monophosphonium salts [1-Ph 2 P(C 10 H 6 )-8-PRPh 2 ] + X ± (2 b: R = H, X = CF 3 SO 3 ; 4: R = Me, X = CF 3 SO 3 ; 5: R = C 6 H 5 CH 2 = Bn, X = Br) has been prepared by treatment of 1,8-bis(diphenylphosphino)naphthalene (dppn, 1) with stoichiometric amounts of HSO 3 CF 3 or CH 3 SO 3 CF 3 in CH 2 Cl 2 at +20°C and with C 6 H 5 CH 2 Br in toluene at +80°C. Their X-ray crystal structures show that there is no evidence for dative P ® P + interactions. Instead, steric repulsion deflects the substituent groups to opposite faces of the naphthalene plane [splay angles: +11.4°(2 b), +13.6°(4); +16.7°(5)]. In solution 2 b, 4, and 5 were dynamic according to 31 P, 13 C, and 1 H NMR spectroscopy. The fluxionality of 2 b involves rapid intramolecular proton exchange between the two phosphorus atoms, which slows down at low temperature, whereas the dynamic behaviour of 4 and 5 is interpreted in terms of hindered rotation of the bulky RPh 2 P + groups (R = Me or Bn) about the P±C(naphthyl) bond. Treatment of 1,8-bis(diphenylphosphoryl)naphthalene (dppnO 2 , 6) with HSO 3 CF 3 gave the protonated bis(phosphine oxide), as the triflate salt, dppnO 2 H + CF 3 SO 3 ± (7). The X-ray structure analysis of 7 revealed a highly strained molecule (P1´´´P2 365.5 pm) in which the P=O bonds point to the same face of the naphthalene plane to accommodate the proton. All isolated compounds were characterised by a combination of 31 P, 1 H, and 13 C NMR spectroscopy, IR spectroscopy (7), mass spectrometry and elemental analysis.Phosphonium-Salze von 1,8-Bis(diphenylphosphino)naphthalin: Moleku È lstrukturen und NMR-spektroskopische Untersuchungen Inhaltsu È bersicht. Durch Umsetzung von 1,8-Bis(diphenylphosphino)naphthalin (dppn, 1) mit sto È chiometrischen Mengen HSO 3 CF 3 oder CH 3 SO 3 CF 3 in CH 2 Cl 2 bei +20°C und mit C 6 H 5 CH 2 Br in Toluol bei +80°C wurde eine repra È-sentative Reihe von Diphosphin-Monophosphoniumsalzen [1-Ph 2 P(C 10 H 6 )-8-PRPh 2 ] + X ± (2 b: R = H, X = CF 3 SO 3 ; 4: R = Me, X = CF 3 SO 3 ; 5: R = C 6 H 5 CH 2 = Bn, X = Br) hergestellt. Die Ro È ntgenstrukturanalysen ergeben keine Hinweise auf dative, bindende P ® P + Wechselwirkungen. Stattdessen fu È hrt sterische Abstoûung zu einer Ablenkung der Substituenten auf entgegengesetzte Seiten der NaphthalinEbene [Spreizwinkel: +11.4°(2 b), +13.6°(4); +16.7°(5)]. In Lo È sung zeigten 2 b, 4 und 5 bei 31 P-, 13 C-und 1 H-NMRspektroskopischen Untersuchungen dynamisches Verhalten. Bei 2 b handelt es sich um einen schnellen, intramolekularen Protonenaustausch zwischen den beiden Phosphoratomen, der bei niedrigen Temperaturen verlangsamt ist, wa È hrend das dynamische Verhalten von 4 und 5 durch gehinderte Rotation der sperrigen RPh 2 P + Gruppen (R = Me oder Bn) um die P±C(Naphthyl) Bindung erkla È rt werden kann. Die Umsetzung von 1,8-Bis(diphenylphosphoryl)naphthalin (dppnO 2 , 6) mit HSO 3 CF 3 fu È hrte zum protonierten Bis(phosphinoxid), in Form des Triflatsalzes, dppnO 2 H + CF 3 SO 3 ± (7). Die Ro È ntgenstrukturanalyse von...

Intramolecular pnicogen interactions in phosphorus and arsenic analogues of proton sponges

“…20,21 It was a natural progression that the success of DMAN and its derivatives lead to the study of the effect of replacement of the N atoms by other atoms of the same period 15, the pnicogen or pnictogen period, the contiguous ones being P and As. 21,28,34 Non-covalent interactions are known to be responsible for the conformation of many molecules. [22][23][24][25][26][27][28][29][30] Numerous review articles have appeared devoted to the different aspects of the hydrogen bond that occurred between N atoms after proton trapping, [31][32][33] but so far there are no theoretical studies on pnicogen derivatives, with P and As instead of N atoms in structures similar to DMAN, and how the intramolecular non-covalent interaction between the heteroatoms alters in the absence of that proton.…”

Naphthalene and Related Systems peri‐Substituted by Group 15 and 16 Elements

“…[18] Quaternization reactions of bis(diorganylphosphines) with a range of alkylating agents showed that only single alkylation takes place even when an excess of the alkylating reagent was used. [6,7,19] On the other hand, excess of strong Bronsted acid afforded the symmetrically diprotonated species (Scheme 9). [7,19] Dmpn (1 a) is a phosphorus congener of the proton sponge (1,8-bis(dimethylamino)naphthalene, NapA C H T U N G T R E N N U N G (NMe 2 ) 2 ), which has received a lot of attention for its exceptional basicity.…”

“…[6,7,19] On the other hand, excess of strong Bronsted acid afforded the symmetrically diprotonated species (Scheme 9). [7,19] Dmpn (1 a) is a phosphorus congener of the proton sponge (1,8-bis(dimethylamino)naphthalene, NapA C H T U N G T R E N N U N G (NMe 2 ) 2 ), which has received a lot of attention for its exceptional basicity. [2] The basicity of dmpn 1 a has not been studied in detail though.…”

“…[7] Importantly, X-ray diffraction shows no evidence for dative P!P + interactions in these compounds. [19] Treatment of 4 f with HOTf affords the protonated bis(phosphine oxide), the X-ray study of which shows the proton is in a bridging position between the two terminal oxygen atoms. [19] Clean reaction of dppn with P 2 I 4 confirmed the stereochemical suitability of the naphthalene-1,8-diyl motif for stabilisation of the cationic low-coordinate triphosphenium motif 5 (Scheme 10).…”

“…[19] Treatment of 4 f with HOTf affords the protonated bis(phosphine oxide), the X-ray study of which shows the proton is in a bridging position between the two terminal oxygen atoms. [19] Clean reaction of dppn with P 2 I 4 confirmed the stereochemical suitability of the naphthalene-1,8-diyl motif for stabilisation of the cationic low-coordinate triphosphenium motif 5 (Scheme 10). No reaction was observed between anthracene-1,8-diyl analogue 6 and P 2 I 4 , perhaps reflecting the too wide "bite angle" of the anthracene ligand.…”