The Relative Stabilities of 1,3‐Diphospha‐2‐silaallene and Some of Its Isomers

Abstract

An ab initio investigation of the relative stability of 1,3‐diphospha‐2‐silaallenes (RP=Si=PR) with respect to potential isomers shows that the allene isomer is not the global minimum throughout a series of several substituents (R = H, SiH3, CH3, Ph, F) — the siladiphosphirene isomer is significantly more stable for all these substituents. The stability of the diphosphasilaallene relative to other isomers depends on the nature of the adjacent substituents. Thus, for simple carbon and silyl substituents alternative ring‐closed isomers are favored over the diphosphasilaallene, which, depending on the substituent, can show silylene or phosphasilene character. The results obtained at the DFT level are compared with those at other levels of theory for the parent system. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Advances in Phosphasilene Chemistry

“…According to DFT calculations (B3LYP/6–311 g(d) level of theory), the stability of symmetric 1,3‐diphospha‐2‐silaallenes VII (R=H, SiH 3 , CH 3 , Ph, F) largely depends on the nature of the substituents at the phosphorus atoms. The molecules display bent structures with the P‐Si‐P bond angles ranging from 168.87° (Si−P distance 2.060 Å) for R=H to 135.46° (Si−P distance 2.12 Å) for R=F), suggesting a possible contribution of a silylone structure (RP→Si←PR) into the ground state of the molecule.…”

“…The molecules display bent structures with the P‐Si‐P bond angles ranging from 168.87° (Si−P distance 2.060 Å) for R=H to 135.46° (Si−P distance 2.12 Å) for R=F), suggesting a possible contribution of a silylone structure (RP→Si←PR) into the ground state of the molecule. Compared to other possible structural isomers, including phosphasilynes R 2 PSi≡P, allenes VII represent only a local minimum structure, whereas the markedly most stable structure is the siladiphosphirene VIII (Figure ) …”

“…[50] In contrast to analogous 1,3-diphosphaallenes (RP=C=PR) [51] and trisilaallenes (R 2 Si=Si=SiR 2 ), [52] neutral1 ,3-diphospha-2-silaallenes VII ( Figure 12) with cumulated Si=Pb onds are not known and for years have remained at arget of main group chemists. [53] According to DFT calculations (B3LYP/6-311g(d) level of theory), [54] the stabilityofsymmetric 1,3-diphospha-2-silaallenes VII (R = H, SiH 3 ,C H 3 ,P h, F) largely depends on the nature of the substituents at the phosphorus atoms. The molecules display bent structuresw ith the P-Si-P bond angles ranging from 168.878 (SiÀPd istance 2.060 )f or R = Ht o1 35.468 (SiÀPd istance 2.12 )f or R = F), suggesting ap ossible contribution of as ilylone structure (RP!Si !…”

“…Compared to other possible structurali somers, including phosphasilynesR 2 PSiP, allenes VII represent only al ocal minimum structure,w hereas the markedly most stable structure is the siladiphosphirene VIII ( Figure 12). [54] 2.1.6. Phosphasilenes with afour-coordinate silicon atom Coordination of aL ewis base to the silicon atom generally increasest he stability of phosphasilenes and, consequently,d ecreasest he double-bond character of the Si=Pb ond through the dominant contributiono fazwitterionic electronic resonance structure with an egatively charged phosphorus atom ( Figure 13).…”

In silico quest for stable phosphastannaallenes

“…The singlet-triplet energy separation was estimated for XCPSi [13] and CPSiX [14] systems by ab initio and DFT calculations as a function of electronegativity of the X atom (X = F, Cl, Br, I). The stability of 1,3-diphospha-2-silaallenes -P Si P-relatively to possible isomers was also investigated through theoretical calculations [15].…”