Wolf-Walther du Mont

Amination of the C‐isopropyldimethylsilyl P‐chlorophosphaalkene (iPrMe₂Si)₂C=PCl (1) leads to the P‐aminophosphaalkenes (iPrMe₂Si)₂C=PN(R)R′ (R, R′ = Me (2), R = H, R′ = nPr (3), R = H, R′ = iPr (4), R = H, R′ = tBu (5), R = H, R′ = 1‐Ada (6), R = H, R′ = CPh₃ (7), R = H, R′ = Ph (8), R = H, RR′ = 2,6‐iPr₂Ph (= DIP) (10), R = H, R′ = 2,4,6‐Me₃Ph (= Mes) (11), R = H, R′ = 2,4,6‐tBu₃Ph (= Mes*)] (12), R = H, R′ = SiMe₃ (13), and R, R′ = SiMe₂Ph (14). ³¹P‐NMR spectra confirm that phosphaalkenes 2–7 and 10–14 are monomeric in solution; the structures of 7, 10, and 12 were determined by X‐ray crystallography. Freshly prepared (iPrMe₂Si)₂C=PN(H)Ph (8) is a monomer that dimerizes with (N→C) proton migration within several hours to the stable diazadiphosphetidine [(iPrMe₂Si)₂CHPNPh]₂ (9). NMR‐scale reactions of deprotonated 5 and 13 with tBuiPrPCl provide by P–P bond formation the P‐phosphanyl iminophosphoranes [(iPrMe₂Si)₂C=](RN=)PPtBu(iPr) [R = tBu (15), R = Me₃Si (17)]. Deprotonated 5 and Me₃GeCl deliver by N–Ge bond formation the aminophosphaalkene (iPrMe₂Si)₂C=PN(tBu)GeMe₃ (20), which with elemental selenium 5 undergoes (N→C) proton migration to form the alkyl(imino)(seleno)phosphorane [(iPrMe₂Si)₂CH](tBuN=)P=Se (21), which is a selenium‐bridged cyclic dimer in the solid state.

Deprotonation of the aminophosphanes Ph₂PN(H)R 1a–1h [R = tBu (1a), 1‐adamantyl (1b), iPr (1c), CPh₃ (1d), Ph (1e), 2,4,6‐Me₃C₆H₂ (Mes) (1f), 2,4,6‐tBu₃C₆H₂ (Mes*) (1g), 2,6‐iPr₂C₆H₃ (DIPP) (1h)], followed by reactions of the phosphanylamide salts Li[Ph₂PNR] 2a, 2b, 2g, and 2h with the P‐chlorophosphaalkene (Me₃Si)₂C=PCl, and of 2a–2g with (iPrMe₂Si)₂C=PCl, gave the isolable P‐phosphanylamino phosphaalkenes (Me₃Si)₂C=PN(R)PPh₂ 3a, 3b, 3g, and (iPrMe₂Si)₂C=PN(R)PPh₂ 4a–4g. ³¹P NMR spectra, supported by X‐ray structure determinations, reveal that in compounds 2a, 2b, 3a, and 3b, with bulky N‐alkyl groups the Si₂C=P–N–P skeleton is non‐planar (orthogonal conformation), whereas 3g, 3h, and 4g with bulky N‐aryl groups exhibit planar conformations of the Si₂C=P–N–P skeleton. Solid 3g and 4g exhibit cisoid orientation of the planar C=P–N–C units (planar I) but in solid 3h the transoid rotamer is present (planar II). From 3g, 4d, and 4g mixtures of rotamers were detected in solution by pairs of ³¹P NMR patterns (3h: line broadening).

Reactions of the (trichlorosilyl)germane Me₃GeSiCl₃ and of the unsymmetric disilane Me₃SiSiCl₃ with the P‐fluorophosphaalkene (Me₃Si)₂C=PF (1) proceed with transfer of SiCl₂ (2) leading to the new C‐dichlorofluorosilyl‐functionalized dialkyldiphosphene (Cl₂FSi)(Me₃Si)₂CP=PC(SiCl₂F)(SiMe₃)₂ (6), which was characterized by X‐ray crystallography. The P‐phosphanylphosphaalkene (Me₃Si)₂C=PP[C(SiCl₂F)(SiMe₃)₂]SiCl₂F (8a) was detected in the reaction mixtures by ³¹P NMR spectroscopy, accompanied by its isomer 8b, presumably (Cl₂FSi)(Me₃Si)C=PP[C(SiCl₂F)(SiMe₃)₂]SiMe₃. The unsymmetric dimers 8a and 8b rearrange by a 1,3‐(P→C) silyl group shift, providing the inversion‐symmetric diphosphene 6. Compound 6 was transformed with selenium into a selenadiphosphirane (9). Quantum chemical calculations were performed on intermediates on the route from 1 and 2 to the metastable unsymmetric dimers 8a and 8b. The addition of SiCl₂ to the P=C bond of 1, followed by ring opening of the silaphosphirane 4, provides the phosphinidene (Me₃Si)₂(Cl₂FSi)CP (5), which rearranges further to isomeric P‐silylphosphaalkenes (Me₃Si)₂C=PSiCl₂F (7a) and (Cl₂FSi)(Me₃Si)C=PSiMe₃ (7b). Rapid phosphinidene–phosphaalkene P–P coupling reactions of 5 with 7a and with 7b followed by 1,2‐(P→P) silyl group shift of ylide‐type dimers 11a and 11b explain the formation of the observed species 8a and 8b. The absence of species related to 8b in previous experiments on the reactions of the P‐chlorophosphaalkene (Me₃Si)₂C=PCl (1′) with Si₂Cl₆, with Me₃GeSiCl₃, and with Me₃SiSiCl₃, allows us to suggest that in the P‐chlorophosphaalkene case nucleophile‐supported SiCl₂ insertion into the P–Cl bond or the substitutive Cl^–/SiCl₃^– exchange are the preferred routes to the metastable P‐(trichlorosilyl)phosphaalkene (Me₃Si)₂C=PSiCl₃.

GRAPHICAL ABSTRACT ABSTRACT The dehydrochlorination of the dichlorophosphane (iPrMe₂Si)₂C(H)PCl₂ (2) with 1,4-diazabicyclo[2.2.2]octane (DBO) provides the P-chlorophosphaalkene (iPrMe₂Si)₂C=PCl (3). Halide exchange reactions of 3 with AgBF₄, with Me₃SiBr, and with Me₃SiI lead to the P-halogenophosphaalkenes (iPrMe₂Si)₂C=PX (X = F: 4; X = Br: 5; X = I: 6). From the reaction of 3 with AgCN, the sterically stabilized P-cyanophosphaalkene (iPrMe₂Si)₂C=P-CN (7) was isolated. The structures of the related P-fluorenylphosphaalkene 9 (from 3 with fluorenyllithium) and of the P-selenophosphaalkenes (iPrMe₂Si)₂C = PSe(2,4,6-tBu₃C₆H₂) (10) and [(iPrMe₂Si)₂C=P]₂Se (11) were determined by X-ray crystallography.

In the RhCl chelate complexes ofC‐bis(trimethylsilyl)‐P‐alkyl(diphenylphosphanyl)aminophosphaalkenes1[(Me₃Si)₂C=PN(R)PPh₂;1a: R = 1‐Ada;1b: R =tBu], the P=C double bonds are preferentially η²‐(P,C)‐coordinated to Rh^I, as shown by the structure determination oftrans‐[RhCl{(Me₃Si)₂C=PN(R)PPh₂}]₂(5a) and by the comparison of the³¹P NMR spectra ofcis‐andtrans‐[RhCl{(Me₃Si)₂C=PN(R)PPh₂}]₂(5a,b), [RhCl(PPh₃){(Me₃Si)₂C=PN(R)PPh₂}] (6a,b), [RhCl(CO){(Me₃Si)₂C=PN(R)PPh₂}] (7a,b) and [(cod)Rh(μ‐Cl)₂Rh{(Me₃Si)₂C=PN(R)PPh₂}] (8a,b). With excess of [RhCl(cod)]₂, the ligand (Me₃Si)₂C=PN(CH₂Ph)PPh₂(1c) forms solid trinuclear complex10containing two Rh(Cl)cod moieties attached to the central chelate unit [Rh(Cl)(1c)]: one Rh atom is attached by (terminal) P→Rh(Cl)cod coordination and the other one by bridging Rh(μ‐Cl)₂Rhcod. The reactions of the complex [RhCl(CO)(PPh₃)₂] with ligands1aor1bunexpectedly led, with elimination of bis(trimethylsilyl)ketene, to racemic Rh^III–chloro complexes [RhCl({Ph₂PN(R)P}₂C(SiMe₃)₂)] (11a,b) containing the dianionic tetradentate chelating “bis‐PNP” ligands (Me₃Si)₂C{P^(–)N(R)PPh₂}₂(12a,b) η⁴‐coordinated to Rh^III(CN 5). The CO‐induced formation of Rh^IIIcomplexes11aand11balso occurred when7aand7bwere treated with another equivalent of ligand1aor1b, when [RhCl(CO)₂]₂was mixed with more than 2 equiv. of1aor1b, and even bubbling gaseous CO into a solution containing6aprovided11aand bis(trimethylsilyl)ketene.

Reactions of P‐chlorophosphaalkenes (RMe₂Si)₂C=PCl (1a: R = Me; 1b: R = Ph) with the disilane Me₃SiSiCl₃ (5) furnish diphosphenes (Cl₃Si)(RMe₂Si)₂C–P=P–C(SiCl₃)(SiMe₂R)₂ (4a: R = Me; 4b: R = Ph) by Me₃SiCl elimination. The structure of the new compound 4b was confirmed by X‐ray diffraction; it displays crystallographic inversion symmetry. Monitoring the reactions with ³¹P‐ and ²⁹Si‐NMR spectroscopy detected P‐(trichlorosilyl)phosphaalkenes (RMe₂Si)₂C=PSiCl₃ (2a, R = Me; 2b, R = Ph) as the primary intermediates from reductive P‐silylation of 4a, 4b, and P‐[(trichlorosilyl)phosphanyl]phosphaalkenes (RMe₂Si)₂C=P–P(SiCl₃)C(SiCl₃)(SiMe₂R)₂ (3a: R = Me; 3b: R = Ph) as unsymmetric dimerisation products that rearrange to provide 4a, 4b in step III of the reaction sequence. This step (the P→C 1,3‐trichlorosilyl shift reaction) was mimicked by the synthesis of (Me₃Si)₂C=P–P(SiCl₃)tBu (7), which rearranges into an unsymmetric diphosphene tBuP=PC(SiMe₃)₂SiCl₃ (8). The bulkier P‐chlorophosphaalkene (iPrMe₂Si)₂C=PCl (1c) reacts with 5, eliminates Me₃SiCl and thereby provides the first persistent acyclic per‐silylated phosphaalkene (iPrMe₂Si)₂C=PSiCl₃ (2c) in an incomplete reaction. 2c exhibits an exceptionally large NMR coupling ¹J(³¹P,²⁹Si) = ±249 Hz. Within weeks, the mixtures of 1c and 2c undergo decomposition with loss of the P=C functions.