Controlled introduction of functional groups at one P atom in [Cp*Fe(η5-P5)] and release of functionalised phosphines.

By salt metathesis reactions of the anionic complexes of the type [Cp*Fe(η4-P5R)]- (R = tBu (1a), Me (1b), -C[triple bond, length as m-dash]CPh (1c); Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with organic electrophiles (XRFG; X = halogen; RFG = (CH2)3Br, (CH2)4Br, Me) a variety of organo-substituted polyphosphorus ligand complexes of the type [Cp*Fe(η4-P5RRFG)] (2) are obtained. Thereby, organic substituents with different functional groups (FG), such as halogens or nitriles, are introduced. In [Cp*Fe(η4-P5RR')] (2a: R = tBu, R' = (CH2)3Br), the bromine substituent can be easily substituted, leading to functionalized complexes [{Cp*Fe(η4-P5tBu)}(CH2)3{Cp*Fe(η4-P5Me)}] (4) and [Cp*Fe(η4-P5RR')] (5) (R = tBu, R' = (CH2)3PPh2) or by abstraction of a phosphine to the asymmetric substituted phosphine tBu(Bn)P(CH2)3Bn (6). The reaction of the dianionic species [K(dme)2]2[Cp*Fe(η4-P5)] (I') with bromo-nitriles leads to [Cp*Fe{η4-P5((CH2)3CN)2}] (7), allowing the introduction of two functional groups attached to one phosphorus atom. 7 reacts with ZnBr2 in a self-assembly reaction to form the supramolecular compound [Cp*Fe{η4-P5((CH2)3CN)2}ZnBr2]n (8).

Pentaphosphaferrocene-mediated synthesis of asymmetric organo-phosphines starting from white phosphorus.

The synthesis of phosphines is based on white phosphorus, which is usually converted to PCl3, to be afterwards substituted step by step in a non-atomic efficient manner. Herein, we describe an alternative efficient transition metal-mediated process to form asymmetrically substituted phosphines directly from white phosphorus (P4). Thereby, P4 is converted to [Cp*Fe(η5-P5)] (1) (Cp* = η5-C5(CH3)5) in which one of the phosphorus atoms is selectively functionalized to the 1,1-diorgano-substituted complex [Cp*Fe(η4-P5R'R″)] (3). In a subsequent step, the phosphine PR'R″R‴ (R' ≠ R″ ≠ R‴ = alky, aryl) (4) is released by reacting it with a nucleophile R‴M (M = alkali metal) as racemates. The starting material 1 can be regenerated with P4 and can be reused in multiple reaction cycles without isolation of the intermediates, and only the phosphine is distilled off.

The reaction behavior of [Cp2Mo2(CO)4(µ,η2:2-P2)] and [Cp''Ta(CO)2(η4-P4)] towards hydroxide and tert-butyl nucleophiles.

The reaction behavior of [Cp2Mo2(CO)4(µ,η2:2-P2)] (1) and [Cp''Ta(CO)2(η4-P4)] (2), respectively, towards the anions OH- and tBu- are reported. While the reaction of 1 with KOH gives the anionic complex [Cp2Mo2(CO)4(µ-PH2)]- (3) under a formal phosphorus atom abstraction, reaction with LitBu leads to the alkylation product [Cp2Mo2(CO)4(µ,η2:1-PPtBu)]- (4). The reactions of 2 with [IDipp-H][OH] ([IDipp-H]+ = 1,3-bis-(2,6-diisopropyl-phenyl)imidazolium) and LitBu yield [Cp''Ta(CO)2{η3-P4(O)H}]- (5) and [Cp''Ta(CO)2(η3-P4tBu)]- (6), respectively. Compounds 3, 4, 5 and 6 were comprehensively characterized by NMR spectroscopy and X-ray structure analysis.

NHCs as Neutral Donors towards Polyphosphorus Complexes.

The first adducts of NHCs (=N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η5 -P5 )] (1) (Cp*=pentamethyl-cyclopentadienyl) with IMe (=1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp''Ta(CO)2 (η4 -P4 )] (Cp''=1,3-di-tert-butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo-P3 -containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.

Transfer Reagent for Bonding Isomers of Iron Complexes.

The cothermolysis of As4 and [Cp″2Zr(CO)2] (Cp″ = η5-C5H3tBu2) results in the formation of [Cp″2Zr(η1:1-As4)] (1) in high yields and the arsenic-rich complex [(Cp″2Zr)(Cp″Zr)(µ,η2:2:1-As5)] (2) as a minor product. In contrast to yellow arsenic, 1 is a light-stable, weighable and storable arsenic source for subsequent reactions. The transfer reaction of 1 with [Cp‴Fe(µ-Br)]2 (Cp‴ = η5-C5H2tBu3) yields the unprecedented bond isomeric complexes [(Cp‴Fe)2(µ,η4:4-As4)] (3a) and [(Cp‴Fe)2(µ,η4:4-cyclo-As4)] (3b). In contrast, the analogous reaction with the CpBn derivative [CpBnFe(µ-Br)]2 (CpBn = η5-C5(CH2(C6H5)5) leads exclusively to the triple decker complex [(CpBnFe)2(µ,η4:4-As4)] (4) possessing the tetraarsabutadiene-type ligand analogous to 3a. To elucidate the stability of the bonding isomers 3a and 3b, DFT calculations were performed. The oxidation of 4 with AgBF4 affords [(CpBnFe)2(µ,η5:5-As5)][BF4] (5), which is a product expanded by one arsenic atom, instead of the expected complex [(CpBnFe)2(µ,η4:4-cyclo-As4)]+.

Arsenic-Rich Polyarsenides Stabilized by Cp*Fe Fragments.

The redox chemistry of [Cp*Fe(η5 -As5 )] (1, Cp*=η5 -C5 Me5 ) has been investigated by cyclic voltammetry, revealing a redox behavior similar to that of its lighter congener [Cp*Fe(η5 -P5 )]. However, the subsequent chemical reduction of 1 by KH led to the formation of a mixture of novel Asn scaffolds with n up to 18 that are stabilized only by [Cp*Fe] fragments. These include the arsenic-poor triple-decker complex [K(dme)2 ][{Cp*Fe(µ,η2:2 -As2 )}2 ] (2) and the arsenic-rich complexes [K(dme)3 ]2 [(Cp*Fe)2 (µ,η4:4 -As10 )] (3), [K(dme)2 ]2 [(Cp*Fe)2 (µ,η2:2:2:2 -As14 )] (4), and [K(dme)3 ]2 [(Cp*Fe)4 (µ4 ,η4:3:3:2:2:1:1 -As18 )] (5). Compound 4 and the polyarsenide complex 5 are the largest anionic Asn ligand complexes reported thus far. Complexes 2-5 were characterized by single-crystal X-ray diffraction, 1 H NMR spectroscopy, EPR spectroscopy (2), and mass spectrometry. Furthermore, DFT calculations showed that the intermediate [Cp*Fe(η5 -As5 )]- , which is presumably formed first, undergoes fast dimerization to the dianion [(Cp*Fe)2 (µ,η4:4 -As10 )]2- .