Photochemical and Thermal Reactions of a 2H-Azaphosphirene Complex with Isonitriles

Abstract

Photochemical ring opening of {2-[bis(trimethylsilyl)methyl]-3-phenyl-2H-azaphosphirene-κP}pentacarbonyltungsten(0) (1) in diethyl ether in the presence of tert-butyl isocyanide (2) yields the η 1 -1-aza-3-phosphaallene complex 4 at low temperature (-30 °C), the formation of which is explained via a 1,1-addition of 2 with the transiently formed terminal phosphinidene complex 3. Complex 4 decomposed slowly at ambient temperature to furnish the [bis(trimethylsilyl)methyl]cyanophosphane complex 5 and isobutene. The same result was obtained via thermal ring opening of complex 1 at high temperature. In contrast, thermolysis of 1 in the presence of cyclohexyl isocyanide ( 7) afforded the N-cyclohexyl-substituted η 1 -1-aza-3-phosphaallene complex 8. Complexes 4, 5, and 8 were unambiguously characterized by NMR and IR spectroscopy; the structure of complex 5 was established by X-ray crystal structure analysis. The structure of 5 and the energetics of its formation via decomposition of 4 were studied by DFT calculations, thus confirming the proposed reaction course.

Deoxygenation of isocyanates via transient electrophilic terminal phosphinidene complexes: Are strained P‐heterocycles involved?

“…The decomposition of complexes 10a,b via elimination of isobutene to give complexes 11a,b (v) was observed previously for complex 10a [17] (Scheme 4).…”

“…Therefore, we assume that 3-imino-oxaphosphirane complexes 8a,b are transiently formed via [2+1] cyclo-addition of complexes 2a,b with the isocyanate (i), which then decompose to yield the phosphinidene oxide complexes 9a,b and tert-butyl isonitrile (ii). Subsequently, the isonitrile then forms η 1− 1,3-azaphosphaallene complexes 10a,b with complexes 2a,b (iii) as observed earlier [17]. Phosphinidene oxide complexes 9a,b finally dimerize to yield the…”

“…Therefore, we assume that 3imino-oxaphosphirane complexes 8a,b are transiently formed via [2+1] cyclo-addition of complexes 2a,b with the isocyanate (i), which then decompose to yield the phosphinidene oxide complexes 9a,b and tert-butyl isonitrile (ii). Subsequently, the isonitrile then forms η 1− 1,3azaphosphaallene complexes 10a,b with complexes 2a,b (iii) as observed earlier [17] In these reactions, the large influence of the metal fragment on the ratio of cis and trans configurated complexes 3:4 deserves mention: It is 1:2 for tungsten (3b: 4b) and 1:1 for chromium (3a: 4a). The latter ratio might be due to the shorter P Cr (than P-W) distance in the respective phosphinidene complexes and a resulting leveling of steric demands of organic substituent and pentacarbonylchromium fragment at phosporus, which should lead to lesser differentiation in the transition states.…”

Coordination of CO to low-valent phosphorus centres and other related P–C bonding situations. A theoretical case study

“…The same group also provided the rst example of a singlet carbene reacting with CO to form a stable, albeit unusual bent ketene derivative. 11 Unexpected was also the outcome of the reaction of [(CO) 5 M(PR)] with CO 2 as deoxygenation leading to CO and head-to-tail dimers of transient complexes [(CO) 5 M-(OPR)] was observed. On the other hand, the reaction of neutral complexes [(CO) 5 M(PR)] with CO at phosphorus, i.e.…”

Dehydroiodination of Iodo‐ and Diiodomethane by a Transient Phosphinidene Complex

“…Unfortunately, further comparison is limited here since complexes of these phosphaalkenes are unknown. In the case of route a we assume α‐elimination by carbon‐to‐phosphorus H transfer,11 whereas formal HI elimination takes place in the case of route b. A further reaction pathway of complex 6 seems to be loss of I 2 to yield complex 8 ( δ =250.5 ppm, 1 J (W,P)=255.6, 2 J (P,H)=24.2, 2 J (P,H)=11.4, 2 J (P,H)=6.5 Hz; Scheme 3, route c).…”