From Phosphidic to Phosphonium? Umpolung of the P₄‐Bonding Situation in [CpFe(CO)(L)(η¹‐P₄)]⁺ Cations (L=CO or PPh₃)

Abstract

Upon coordinating P4 to electron poor cyclopentadienyl‐iron cations, the average P−P bond distances shrink and the respective P4 breathing mode in the Raman spectra (600 cm−1, P4, free) is blueshifted by >40 cm−1 in [CpFe(CO)(L)(η1‐P4)]+ cations (L=CO or PPh3). Analysis suggests that this corresponds to an umpolung of the bonding from more phosphidic in the known, electron‐rich systems to more phosphonium‐like in the reported electron‐poor versions. This may open new functionalization pathways for white phosphorus P4.

Coordination Chemistry of P4S3 and P4Se3 towards the Iron Fragments [Fe(Cp)(CO)2]+ and [Fe(Cp)(PPh3)(CO)]+

“…Owing to their dynamic nature in solution,t he known silver complexes Ag(P 4 S 3 ) n [WCA] [12,13] and Ag(P 4 Se 3 ) n [WCA] (n = 1, 23 ) [14] show only two distinct signals of the ligandsi nt he 31 PNMR spectra.C omplexes 1 and 2 show three distinct signals of the apical phosphorus atom P a ,t he coordinated basal phosphorus atom P b/coord ,a nd the noncoordi-nated phosphorus atoms P b/noncoord .T his demonstratest hat the P 4 Se 3 and P 4 S 3 cages are firmly bound to the Fp moiety through one of their basal phosphorusa toms, similart ot he more electron-rich analogues [Cp*Ru(L 2 )(P 4 S 3 )] + and [Cp*Ru(L 2 )(P 4 Se 3 )] + (L 2 = bidentate phosphine) but unlike the more weakly bound P 4 ligand in [FpÀP 4 ] + . [3,10] Complex 3 shows five different phosphorus signals, one for the PPh 3 ligand and four fort he P 4 S 3 cage. An apical coordination of the cages would exhibit less cage signals, as known from studies of ruthenium 16 electron fragments coordinated to P 4 S 3 that include am ixture of isomers.…”

“…The shift of P b/coord is stronger in the examples with bisphosphine ligands. [10] 13 CNMR signals of the CO ligandsi nc omplex 1a could not be obtained within ar easonable timeframe, and thus, are not given (but IR and Raman spectroscopy data are available). 31 PNMR spectra of complexes 1, 2,a nd 3 as wellast he free ligands P 4 S 3 and P 4 Se 3 in CD 2 Cl 2 at room temperature.…”

“…Couplings to the protons are omittedi nthis list (see the Supporting Information). [10] Vibrational spectroscopy [b] These spin systems show additional splittings owingt oh igher-order effects.…”

“…Thus, Scheeretal. [10] The formation of these complexes showed that it is possible to use the ligand-transfer reaction to bind weakl igands to these metal fragments through halide abstractions given that the ligand is immediatelypresent in the reactionenvironmentb yc oordination to the silver ion. This acts as as table storage form of yellow arsenic that releases the As 4 cluster upon removal of the Ag + cation with aw ell-soluble halide complex.…”

“…succeeded in the synthesis of complexes of yellow arsenic ([PPh 3 Au(As 4 )] + and [Cp*Ru(dppe)(As 4 )] + )t hrough the reactiono ft he corresponding transition-metal halide with Ag(As 4 ) 2 [Al(OR F ) 4 ]. [10] Yet, quite an umber of complexes of weak and often poorly soluble ligandsw ith the silver ion of Ag[Al(OR F ) 4 ]a re accessible;t hat is, those with inorganic rings, such as S 8 ,S e n (n = 6, 12), and the cages P 4 ,P 4 S 3 ,P 4 Se 3 ,A s 4 S 3 ,a nd As 4 S 4 . [7,8] In this realm, the more electron-poor complex [CpFe(CO) 2 ] + (Fp + )a nd monophosphine-substituted complex [CpFe-(CO)(PPh 3 )] + (FpPPh 3 + )u nits are not knownf or coordination chemistry that uses such weak ligands.…”