An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An overview is given on synthesis and structures of new bidentate phosphaalkene ligands [(RMe2Si)2CP]2E (E=O, NR, N−) and (RMe2Si)2CPN(R′)PR′′2. Exceptional properties of these ligands, extending beyond predictable properties of phosphaalkenes are: (i) the NSi bond cleavage of [(iPrMe2Si)2CP]2NSiMe3 with AuI and RhI chloro complexes under mild conditions leading to binuclear complexes of the 6π-delocalised imidobisphosphaalkene anion [(iPrMe2Si)2CP]2N−, and (ii) the chlorotropic formation of molecular 1:2 PdII and PtII metallochloroylid complexes with novel ylid-type ligands [(RMe2Si)2CP(Cl)N(R)PR2]−, and the transformation of a P-platina-P-chloroylid complex into a C-platina phosphaalkene by intramolecular chlorosilane elimination. Properties of the heavier congeners [(RMe2Si)2CP]2E (E=S, Se, Te, PR, P−, As−) and (RMe2Si)2CPEPR′′2 (E=S, Se, Te) are also described.

Metalation of the aminophosphaalkene (iPrMe(2)Si)(2)C=PN(H)SiMe3 (2) with lithium diisopropylamide (LDA) in THIF solution, followed by the reaction of the lithium salt 3 with the P-chlorophosphaalkenes (RMe2Si)(2)C=PCl (1a, R = Me; 1b, R = iPr; 1c, R = Ph), furnishes the first N-silylimmo-bridged bis(phosphaalkenes) [(iPrMe(2)Si)(2)C=P](2)NSiMe3 (4a) and [(iPrMe(2)Si)(2)C=P][(RMe2Si)(2)C=P]NSiMe3 (4b, R = Me; 4c, R = Ph). The N-Si bond cleavage of 4a under very mild conditions with AuCl(THT) and with [RhCl(COD)](2) provides binuclear Au-1 and Rh-1 complexes 5, 6 of the P, P'-coordinated imidobis(phosphaalkene) anion [(iPrMe(2)Si)(2)C=P](2)N-, the first case of elusive P=C-unsaturated congeners of the "classic" bis(phosphanyl)amide ligands. Solid 4a exists in a helically distorted S-shaped structure with two inequivalent P=C groups, but P-31-NMR reveals the equivalence of both P=C groups in solution at the NMR time scale. The P=C and P-N bonds distances in 4a do not indicate significant conjugation within the C=P-N-P=C moieties whereas in complexes 5 and 6 the W-shaped CPNPC heteropentadienide anion exhibits strong 5-center-6-pi conjugation according to DFT calculations and to the experimental P=C and P=N bond lengths.

Reactions of P-chlorophosphaalkenes (RMe2Si)(2)C=PCl (1a: R = Me; 1b: R = Ph) with the disilane Me3SiSiCl3 (5) furnish diphosphenes (Cl3Si)(RMe2Si)(2)C-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 P-31- and Si-29-NMR spectroscopy detected P(trichlorosilyl)phosphaalkenes (RMe2Si)(2)C=PSiCl3 (2a, R = Me; 2b, R = Ph) as the primary intermediates from reductive P-silylation of 4a, 4b, and P-[(trichlorosilyl)phosphanyl]phosphaalkenes (Rme(2)Si)(2)C=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)(2)C=P-P(SiCl3)tBu (7), which rearranges into an unsymmetric diphosphene tBuP=PC(SiMe3)(2)SiCl3 (8). The bulkier P-chlorophosphaalkene (iPrMe(2)Si)(2)C=PCl (1c) reacts with 5, eliminates Me3SiCl and thereby provides the first persistent acyclic per-silylated phosphaalkene (iPrMe(2)Si)(2)C=PSiCl3 (2c) in an incomplete reaction. 2c exhibits an exceptionally large NMR coupling (1)J(P-31,Si-29) = +/- 249 Hz. Within weeks, the mixtures of 1c and 2c undergo decomposition with loss of the P=C functions.

Hydrolytic cleavage of the P-chlorophosphaalkenes (RMe2Si)2C=PCl (R = Me: 1a; R = iPr: 1b) in the presence of triethylamine leads to di(phosphavinyl) ethers (2,4-diphospha-3-oxapentadienes) [(RMe2Si)2C=P]2O (2a, 2b) as main products, accompanied by alkylphosphinic acids (RMe2Si)2(H)CP(H)(O)OH (3a, 3b). The hydrolysis of (PhMe2Si)2C=PCl (1c) proceeds less selectively. Reactions with metal oxides under aprotic conditions provide 2a [impure, from 1a with (nBu3Sn)2O] and 2b [from iodophosphaalkene (iPrMe2Si)2C=PI with Ag2O] as oils. 1H, 13C, 29Si and 31P NMR spectra, however, allow unambiguous characterisation of 2a and 2b. Formation mechanisms, structure, and C=P-O π stabilisation of the oxabisphosphaalkene [(H3Si)2C=P]2O (2ʹ) were studied with DFT methods. The double [2+4] cycloaddition reaction of 2a with two equivalents of cyclopentadiene leads to the phosphinous anhydride 7 as a mixture of diastereomers whereas the addition of two equivalents of tetrachloro-o-benzoquinone proceeds in a diastereoselective fashion. An X-ray crystal structure determination of the resulting oxo-bridged bis(2-phospha-2,5-dioxa-3,4-benzophospholene) derivative 8 revealed the presence of a racemic mixture of (R,R)- and (S,S)-configurated molecules. The solid state structure of a by-product, bisylphosphonic tetrachlorocatechol monoester (Me3Si)2CH-P(=O)(OH)-o-OC6Cl4OH 9, was also determined crystallographically.