'P' undressed: A stable phosphanylidene phosphorane with a sterically accessible (naked) two‐coordinate P is reported (see structure). Coordination to Pd0 reveals its phosphine donor/phosphinidene acceptor (R3P→PR′) nature by exposing its phosphinidene‐like reactivity.
The reactions of a peri-substitution stabilized phosphanylidene-phosphorane 1 with [AuCl(tht)] or [PtCl2(cod)] afford binuclear complexes [((1)(AuCl)2)2] 2 and [((1)(PtCl2))2] 3, in which four electrons of the ligand are used in bonding to two metal atoms in the bridging arrangement. Reactions of 1 with [Mo(CO)4(nbd)] or (RhCl2Cp*)2 afford mononuclear complexes [(1)2Mo(CO)4] 4 and [(1)RhCl2Cp*] 5, in which two electrons of the ligand are used to form terminal complexes. Formation of these complexes disrupts the negative hyperconjugation at the P-P bond to various extent, which is mirrored by variations in their P-P bond distances (2.179(4)-2.246(4) Å). The P-P bond is ruptured upon formation of the Pd diphosphene complex 6, which is likely to proceed through a phosphinidene intermediate. In air 1 is fully oxidized to phosphonic acid 7. Reactions of 1 with chalcogens under mild conditions generally afford mixtures of products, from which the trithionated 8, dithionated 9, diselenated 10 and monotellurated species 11 were isolated. The bonding in the chalcogeno derivatives is discussed using DFT (B3LYP) and natural bond orbital analysis, which indicates a contribution from a dative bonding in 8-10. The buttressing effect of the peri-backbone is shown to be an essential factor in the formation of the single push-double pull bis(borane) 13. This is demonstrated experimentally through a synthesis parallel to that used to make 13, but lacking the backbone, which leads to different products. The P-P bond distances in the reported products, as well as additional species, are correlated with Wiberg Bond Indices, showing very good agreement for a variety of bonding modes including the negative hyperconjugation.
The fundamental synthetic building blocks FcPH2 and FcPCl2 are obtained in high yield and excellent purities via the fully regiospecific electrophilic monofunctionalisation of ferrocene with P4S10, thus replacing inconvenient tBuLi based procedures.
Acyl oximes derived from a variety of indolylalkanones underwent a ring closure sequence during FVP to afford 9H-pyrido[2,3-b]indoles. Unlike UV light promoted reactions of oxime esters, the mechanism is almost certainly not mediated by iminyl radicals but probably involves tautomerism, elimination of acetic acid, and a final electrocyclic ring closure.
Bis(borane) adducts Acenap(PiPr2·BH3)(PRH·BH3) (Acenap = acenaphthene-5,6-diyl; 4a, R = Ph; 4b, R = ferrocenyl, Fc; 4c, R = H) were synthesised by the reaction of excess H3B·SMe2 with either phosphino-phosphonium salts [Acenap(PiPr2)(PR)](+)Cl(-) (1a, R = Ph; 1b, R = Fc), or bis(phosphine) Acenap(PiPr2)(PH2) (3). Bis(borane) adducts 4a-c were found to undergo dihydrogen elimination at room temperature, this spontaneous catalyst-free phosphine-borane dehydrocoupling yields BH2 bridged species Acenap(PiPr2)(μ-BH2)(PR·BH3) (5a, R = Ph; 5b, R = Fc; 5c, R = H). Thermolysis of 5c results in loss of the terminal borane moiety to afford Acenap(PiPr2)(μ-BH2)(PH) (14). Single crystal X-ray structures of 3, 4b and 5a-c are reported.
Phosphanylidene-s 4 -phosphoranes (RP = PR' 3 ) are phosphorus analogues of alkylidene-s 4 -phosphoranes (R 2 C = PR' 3 ), better known as Wittig reagents. Phosphanylidene-s 4 -phosphoranes are synthetically accessible in the free form (RP= PR' 3 ) and also in the transition-metal-stabilized form (L n M ! P(R) = PR' 3 ).[1] The latter complexes are commonly used in both P = C bond generation and as a source of the phosphinidene (R-P) moiety in the continuing pursuit of new terminal phosphinidene complexes R-P=ML n . In marked contrast, free phosphanylidene-s 4 -phosphoranes have received little attention because isolable (i.e., thermally stable) examples remain rare.[2-4] Herein we report the synthesis and structure of the stable cyclic phosphanylidenes 4 -phosphorane 3 (see Scheme 1). Compound 3 possesses a sterically nonhindered phosphanylidene moiety, yet it is thermally stable enough to be isolated and stored at room temperature. The potential diversity of the coordination chemistry of 3 is illustrated by its transition-metal (Pd 0 ) complex and bis(borane) adduct.Recently, we synthesized the first "bottleable" (i.e., room temperature stable) phosphine-phosphine donor-acceptor (DA) complex 1.[5] Because of their normally low thermal stability, the reactivity of phosphine-phosphine complexes (other than thermal decomposition pathways) is virtually unknown. Having access to 1, we set off to investigate its chemistry in detail. We were especially intrigued by the possibility of utilizing 1 as a precursor for compounds with a low-coordinate phosphorus atom in the peri position, since no compounds of this type had been reported in the literature.[6] We postulated that the specific peri arrangement of the relatively basic PiPr 2 group and the reactive dihalophosphine group should make 1 a good source of "across the peri gap" donor-stabilized, low-valent phosphorus species.The initial reactivity screen of 1 towards reducing reagents revealed that the reaction with BH 3 ·Me 2 S proceeded cleanly, giving the bis(borane) adduct 2 (d P = 13.6 and 43.9 ppm, 1 J PP = 198.5 Hz) in almost quantitative yield (Scheme 1). Although 2 does not possess a low-coordinate phosphorus center, the single-crystal X-ray structure (Figure 1) [7] confirmed an interesting bonding situation in which a Lewisbase-stabilized phosphinidene moiety acts as a double donor towards two Lewis-acidic (borane) moieties. Two representative resonance forms of 2 (zwitterionic and with DA bonding) are shown in Scheme 2. The P1ÀP2 distance in 2 (2.2208(11) ), is consistent with a P À P single bond. The P2 À B1 and P2 À B2 distances [1.943(5) and 1.943(4) , respectively] are equal and are also as expected for P À B single bonds (typical range 1.90 to 1.95 ). As mentioned recently by Protasiewicz and co-workers, [2d] whilst of fundamental interest, no bis(borane) push-pull phosphinidene systems have been structurally characterized and compound 2 thus Scheme 1. Synthesis and selected reactivity of the phosphanylidene phosphorane 3. Figure 1. Molecular structu...
A series of phosphorus-arsenic peri-substituted acenaphthene species have been isolated and fully characterised, including single crystal X-ray diffraction. Reactions of EBr3 (E = P, As) with iPr2PAcenapLi (Acenap = acenaphthene-5,6-diyl) afforded the thermally stable peri-substitution supported donor–acceptor complexes, iPr2PAcenapEBr23 and 4. Both complexes show a strong P→E dative interaction, as observed by X-ray crystallography and 31P NMR spectroscopy. DFT calculations indicated the unusual As∙∙∙As contact (3.50 Å) observed in the solid state structure of 4 results from dispersion forces rather than metallic interactions. Incorporation of the excess AsBr3 in the crystal structure of 3 promotes the formation of the ion separated species [iPr2PAcenapAsBr]+Br− 5. A decomposition product 6 containing the rare [As6Br8]2– heterocubane dianion was isolated and characterised crystallographically. The reaction between iPr2PAcenapLi and EtAsI2 afforded tertiary arsine (BrAcenap)2AsEt 7, which was subsequently lithiated and reacted with PhPCl2 and Ph2PCl to afford cyclic PhP(Acenap)2AsEt 8 and acyclic EtAs(AcenapPPh2)2 9.
A series of novel ferrocenyl-and aryl-phosphonofluorodithioic salts, adducts, and esters has been prepared. The reaction of 2,4-diferrocenyl-1,3,2,4-diathiadiphosphetane 2,4-disulfide {[FcP(μ-S)S]2, FcLR} with dry KF or tetrabutylammonium fluoride (TBAF) led to the corresponding potassium and tetrabutylammonium salts of ferrocenyldithiofluorophosphinic acids. Treating potassium ferrocenyldithiofluorophosphinic acid with an equimolar amount of tetraphenylphosphonium chloride readily yielded the corresponding organic adducts, and with mono-and di-halogenated alkanes generated a series of the corresponding esters of ferrocenylphosphonofluoridodithioates. Similarly, using 1,3-epithionaphtho [1,8-cd]
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