Synthesis of Li/OR phosphinidenoid complexes: on the evidence for intramolecular O–Li donation and the effect of cation encapsulation

Abstract

Synthesis of phosphinite complexes 12-14a-c, 15a and 16a was achieved via reaction of transient Li/Cl phosphinidenoid complexes 6-10, prepared from dichloro(organo)phosphane complexes [(OC)5M{RPCl2}] 1-5 (1,6: R = CPh3, 2,7: R = C5Me5, 3-5, 8-10: R = CH(SiMe3)2, 1-3, 6-8: M = W, 9: M = Mo, 10: M = Cr), with different alcohols 11a-c (a: R = allyl, b: R = methyl, c: R = isopropyl). Deprotonation of complexes 12b, 13b with MeLi or (t)BuLi in the presence of two equivalents of 12-crown-4 led to the selective formation of phosphinidenoid complexes [Li(12-crown-4)2] [(OC)5W{RP(OCH3)}] (18a R = CPh3 and 18b R = C5Me5) which were stable in solution at ambient temperature, in contrast to Li/OMe phosphinidenoid complexes without 12-crown-4. To our surprise attempts to crystallise complex 18b yielded complex 21 having a Li-O-P subunit. The reaction of complex 17c with [Ph3C]BF4 yielded the P-C coupling product 26 and, hence, the first evidence for an oxidative SET reaction. All isolated products were characterised by multinuclear NMR spectroscopy, IR, MS and single-crystal X-ray crystallography in the case of complexes 12a,b, 13b, 14a-c, 15a, 16a and 21.

Synthesis and Deprotonation of Aminophosphane Complexes: First K/N(H)R Phosphinidenoid Complexes and Access to a Complex with a P2N‐Ring Ligand

“…We observed that the chemical shift and the coupling constant ( 1 J ) magnitude was dependent on the organic substituent at the nitrogen center. Consistent with the trend observed for phosphinite complexes, a trend for high‐field‐shifted resonances was observed with the increase of steric demand at the nitrogen center (Me> i Pr> t Bu). The observed resonance signals of complexes 3 a – e are shifted downfield compared to the previously reported aminophosphane complexes, which were obtained by a thermal reaction of a 7‐phosphanorbornadiene complex or a 2 H ‐azaphosphirene complex with amines.…”

“…), which has attracted considerable attention owing to the versatile construction of useful building blocks . A similar insertion reaction of Li/Cl phosphinidenoid complexes into the O−H bonds of alcohol derivatives to yield phosphinite complexes was reported recently . In contrast to extensive investigations on carbenoid insertions into N−H bonds, similar reactions of silylenoid compounds are much less investigated and are completely unknown for M/X phosphinidenoid complexes.…”

“…The 31 P NMR resonances of the K/NHR phosphinidenoid complexes 4 c ( δ =90.6 ppm, 1 J P,W =98.3 Hz) and 4 e ( δ =91.1 ppm, 1 J P,W =100.2 Hz) were observed at lower field compared with their precursors ( 3 c : δ =37.2 ppm, 1 J P,W =263.8 Hz; 3 e : δ =54.6 ppm, 1 J P,W =264.5 Hz), but they were significantly high‐field‐shifted compared with the related Li/Cl and Li/OMe phosphinidenoid complexes (R=CPh 3 : δ =252.0 and 289.5 ppm, 1 J P,W =77.6 and 84.0 Hz, respectively). Both phosphinidenoid complexes 4 c and e displayed significantly larger 1 J P,C coupling constant magnitudes compared with complexes 3 c and e (61.6 and 52.9 Hz vs. 7.1 and 12.5 Hz, respectively).…”

“…The molecular structures of 3 b – e were determined by single‐crystal X‐ray diffraction studies and are presented in Figure ( 3 c ) and ( 3 e ) (see the Supporting Information for structures of 3 b and d ). Similar to the geometry of phosphinite complexes, the phosphorus centers have a trigonal geometry with a bond angle sum of 340.31 ( 3 c ) and 341.05° ( 3 e ) (this includes the W(CO) 5 fragment and not the P−H unit). Both complexes show similar P−W bond lengths compared to the analogous P−CH(SiMe 3 ) 2 ‐substituted aminophosphane complexes, whereas significant bond elongation was observed for the P−C bond: 1.918(2) ( 3 c ) and 1.897(3) Å ( 3 e ) versus 1.835(13) Å .…”

“…By comparison, Li/OR and Li/NR 2 phosphinidenoid tungsten(0) complexes are much less investigated, and their reactivity remains largely unexplored. Li/OR phosphinidenoid tungsten(0) complexes display a higher thermal stability than their chloro counterparts, which can be enhanced by cation encapsulation to form the cation [Li(12‐crown‐4) 2 ] + . In contrast, Li/NR 2 and Na/NR 2 tungsten(0) complexes that bear the same phosphorus substituent suffered from decomposition in solution …”