Imino‐Bridged Bisphosphaalkenes (2,4‐Diphospha‐3‐azapentadienes)

Abstract

Deprotonation of aminophosphaalkenes (RMe(2)Si)(2)C=PN(H)(R') (R=Me, iPr; R'=tBu, 1-adamantyl (1-Ada), 2,4,6-tBu(3)C(6)H(2) (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe(2)Si)(2)C=P(M)(R')] with one equivalent of the corresponding P-chlorophosphaalkenes (RMe(2)Si)(2)C=PCl provides bisphosphaalkenes (2,4-diphospha-3-azapentadienes) [(RMe(2)Si)(2)C=P](2)NR'. The thermally unstable tert-butyliminobisphosphaalkene [(Me(3)Si)(2)C=P](2)NtBu (4 a) undergoes isomerisation reactions by Me(3)Si-group migration that lead to mixtures of four-membered heterocyles, but in the presence of an excess amount of (Me(3)Si)(2)C=PCl, 4 a furnishes an azatriphosphabicyclohexene C(3)(SiMe(3))(5)P(3)NtBu (5) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P=C double bond and an exocyclic ylidic P((+))-C((-))(SiMe(3))(2) unit. Using the bulkier iPrMe(2)Si substituents at three-coordinated carbon leads to slightly enhanced thermal stability of 2,4-diphospha-3-azapentadienes [(iPrMe(2)Si)(2)C=P](2)NR' (R'=tBu: 4 b; R'=1-Ada: 8). According to a low-temperature crystal-structure determination, 8 adopts a non-planar structure with two distinctly differently oriented P=C sites, but (31)P NMR spectra in solution exhibit singlet signals. (31)P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6-tBu(3)C(6)H(2)) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P-N bonds in persistent compounds [(RMe(2)Si)(2)C=P](2)NMes* (11 a, 11 b). DFT calculations for the parent molecule [(H(3)Si)(2)C=P](2)NCH(3) suggest that the non-planar distortion of compound 8 will have steric grounds.

Exceptional Coordination Mode of Unsaturated PNP Ligands (Me3Si)2C=PN(R)PPh2 with Palladium and Platinum Dichlorides: Insertion of Phosphaalkene Phosphorus Atoms into Metal–Chlorine Bonds

“…- [10,11] with R 2 PCl led preferentially via P-P bond formation to the undesired phosphanylphosphorane iso- Scheme 1. mers (Me 3 Si) 2 C=P(=NtBu)PR 2 .…”

Access to Metal Complexes of the Elusive Imidobis(phosphaalkene) Anion by N–Si Bond Cleavage of a N‐Silylimino‐Bridged Bis(phosphaalkene)

“…[2] The electronegative nitrogen substituent is expected to enhance the π-acceptor properties of the P=C bond [3] in type A and C ligands. [4] The recent observation, that bidentate type A ligands undergo unusual phosphorus insertion reactions into Pd-Cl and Pt-Cl bonds leading to unique metalla(chloro)ylid chelate complexes, [4] gave rise to the expectation that stable iminobis(phosphaalkenes) may also exhibit unusual behaviour as ligands in transition metal chemistry, and N-silyl derivatives (C) might even be potential precursors of the elusive 2,4-diphospha-3-azapentadienide anion [(Me 3 Si) 2 C=P] 2 N -(D), [5] the P=C-unsaturated counterpart of the widely used bis(phosphanyl)amides (R 2 P) 2 N -. [6] [a] Institut für Anorganische und Analytische Chemie der Technischen Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany [b] Department of Inorganic and Analytical Chemistry, Budapestcase of elusive P=C-unsaturated congeners of the "classic" bis(phosphanyl)amide ligands.…”

Nitrogen- and oxygen-bridged bidentate phosphaalkene ligands

“…Metalated aminophosphaalkenes Li[(RMe 2 Si) 2 C PNtBu] (3a: R = Me; 3b: R = iPr) react with the corresponding P-chlorophosphaalkenes at low temperatures, furnishing solutions of the desired tbutylimino-bridged bisphosphaalkenes 5a, 5b (Scheme 2), which exhibit singlet signals in 31 P-NMR [13]. Raising the temperature to 0 8C and above leads to formation of products from rearrangement reactions indicated by the occurence of one or more [ ( S c h e m e _ 1 ) T D $ F I G ] Scheme 1.…”

“…In the context of possible application in catalysis, however, the O-and N-bridged ''P C-unsaturated'' compounds (type C) related to classic ''saturated PNP'' ligands (Ph 2 P) 2 NR appear to be particularly attractive goals. This expectation gave the incentive to focus on novel type C N-and O-bridged bisphosphaalkenes [12,13] and on type D phosphanylaminophosphaalkenes (Me 3 Si) 2 C PN(R)PR 0 2 [14]. In this overview, recent results on type C structures [(RMe 2 Si) 2 C P] 2 E (E = O, NR, N À ) will be presented in Section 2 and properties of type D ligands (RMe 2 Si) 2 C P-N(R)-PR 2 and related compounds will be discussed subseqently (Section 3).…”

“…These reactions are based on the new starting material (iPrMe 2 Si) 2 C PCl 4b [18,19]. To improve crystallisation properties of thermolabile N-alkyl products, N-1-adamantyl derivatives were also used [13].…”