Complexes of Azaphospholes: Synthesis and Structure of Pentacarbonyl-(η1)-2-phosphaindolizine)chromium(0), -molybdenum(0), and -tungsten(0)

Abstract

The complex chemical behaviour of 2‐phosphaindolizines 1 (1,3‐azaphospholo[1,5‐a]pyridines) towards metal carbonyl compounds was studied. (η1‐2‐Phosphaindolizine)M(CO)5 complexes 2–4 (M = Cr, Mo, W) were formed from 1 and [(THF)M(CO)5], the cis‐L2Cr(CO)4 complex 5f from 1f and tetracarbonyl(norbornadiene) chromium(0). The reaction of 2‐phosphaindolizines 1e, 1f, or 1g with tricarbonyl(cycloheptatriene)molybdenum(0) or tricarbonyl(mesitylene)tungsten(0) yielded σ‐complexes of the types L2M(CO)4or L3M(CO)3 rather than isolable π‐complexes. In one case a strong upfield signal (δ31P = 6.1) was observed with a coordination shift of Δδ = –161.7, which is typical for π‐coordination. Prolonged reaction or work‐up led, however, to dismutation yielding 1g and the fac‐L3Mo(CO)3 complex 6g. X‐ray structure analysis of 2a indicates an increased 10π‐delocalization compared with 1a and a changed conformation of the acyl substituent. The influence of substituents and metals on the 31P and 13C complexation chemical shifts and coupling constants is discussed.

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η1-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

“…Coordination of the σ 2 ,λ 3 -P atom of 2-phosphaindolizine to ( O -menthoxy)aluminium dichloride causes a downfield shift in the 31 P NMR signal by δ 34–55 ppm, which is in accordance with the previous results [26–27]. An attempt to isolate the complex was, however, unsuccessful.…”

“…Furthermore, it has been established by X-ray crystal structure studies that Cr(CO) 5 is coordinated to the phosphorus atom only, and no chelate complex involving the σ 2 ,λ 3 -P atom and carbonyl oxygen atom is formed [27]. As reported recently, the DFT calculations reveal that the activation energy of the DA reaction is lowered only if the aluminium catalyst is coordinated to the phosphorus atom; when it is coordinated to the carbonyl oxygen atom, the activation energy barrier is rather high as compared to that for the DA reaction of the uncomplexed 2-phosphaindolizine [42].…”

Metalated 1,3-Azaphospholes:1H-1,3-Benzazaphosphole and 1,3-Benzazaphospholide Tungsten(0) and Tungsten(II) Complexes

“…The tungsten pentacarbonyl complex 4 even displays a negative coordination shift (Δδ = −35.0). The upfield shift of the tungsten relative to the related chromium complex reflects the typical core‐effect in transition metal phosphane complexes25 and is also observed for related (phosphaindolizine)metallapentacarbonyls (M = Cr, Mo, W) 26. The one bond 31 P− 183 W coupling constant is much larger than in 2 , 5 and 6 and similar to that in pentacarbonyltungsten complexes of less‐basic triorganophosphanes 25.…”

Syntheses of 2‐Unsubstituted 1H‐1,3‐Benzazaphospholes from N‐Formyl‐2‐bromoanilides

“…The tungsten atoms deviate from the ring planes by 0.33 Å, corresponding to 7.5° and 7.8° angles of the P—W vectors to the ring planes. In structurally related Cr(CO) 5 complexes with 1,5‐dimethyl‐1,2,3‐diazaphosphole and pivaloyl‐2‐phosphaindolizine ligands, where phosphorus profits less from the π‐donor effect of the σ 3 N atom, the deviation of the P–Cr bonds from the ring planes are small and not more significant, 2° and 1.5°/0.12 Å , respectively, as they are in the known o ‐substituted phosphinine W(CO) 5 complexes (0.7–3.3°/0.02–0.12 Å) . The W—C bonds trans to the benzazaphospholes are shortened and the trans ‐C—O bonds elongated as compared with the corresponding bonds of cis ‐CO ligands.…”