Synthesis and Thermolysis of the Homoleptic Iron(II) Complex [Fe{cyclo-(P5tBu4)}2]

Coordination Chemistry of Hepta-tert-butylnonaphosphane

Hepta-tert-butylnonaphosphane {cyclo-(P4tBu3)}2PtBu was employed as a ligand in transition metal complexes of iron(0) (1), cobalt(–I) (2), copper(I) (3) and rhodium(I) (4), which are readily formed in moderate to good yields,...

Gold(I) Complexes of Tetra-tert-butylcyclotetraphosphane

The reaction of tetra-tert-butylcyclotetraphosphane cyclo-(PtBu)4 (L) with one to four equivalents [AuCl(tht)] (tht = tetrahydrothiophene) leads to the gold(I) complexes [(AuCl)nL] (n = 1–4, 1–4) in which the ligand coordinates...

Facile synthesis of cyclo-(P4tBu3)-containing oligo- and pnictaphosphanes

The cyclo-(P₄^tBu₃) synthon [Li{cyclo-(P₄^tBu₃)}(thf)(tmeda)] (1) (thf = tetrahydrofuran, tmeda = N,N,N',N'-tetramethylethane-1,2-diamine) is readily accessible in a one-pot synthesis from P₄ and Li^tBu. The use of 1 as a cyclo-(P₄^tBu₃) building block enables the rational synthesis of cyclo-(P₄^tBu₃)-containing oligophosphanes, namely {cyclo-(P₄^tBu₃)}₂ (2), {cyclo-(P₄^tBu₃)}₂P^tBu (3) and {cyclo-(P₄^tBu₃)}₂CH₂ (4), C_3v-symmetric pnictaphosphanes E{cyclo-(P₄^tBu₃)}₃ (E = Bi, Sb, As; 5-7) as well as AsCl{cyclo-(P₄^tBu₃)}₂ (8). Compounds 5 and 6 represent the first neutral homoleptic bismuthane and stibane that contain only bonds to phosphorus. All new compounds were isolated in moderate to good yields and fully characterised. The ³¹P{¹H} NMR spectral data of 1, 2, 4, and 8 have been determined by automated line-shape analysis.

Homoleptic mono-, di-, and tetra-iron complexes featuring phosphido ligands: a synthetic, structural, and spectroscopic study

We report the first series of homoleptic phosphido iron complexes synthesized by treating either the β-diketiminato complex [(Dippnacnac)FeCl₂Li(dme)₂] (Dippnacnac = HC[(CMe)N(C₆H₃-2,6-iPr₂)]₂) or [FeBr₂(thf)₂] with an excess of phosphides R₂PLi (R = tBu, tBuPh, Cy, iPr). Reaction outcomes depend strongly on the bulkiness of the phosphido ligands. The use of tBu₂PLi precursor led to an anionic diiron complex 1 encompassing a planar Fe₂P₂ core with two bridging and two terminal phosphido ligands. An analogous reaction employing less sterically demanding phosphides, tBuPhPLi and Cy₂PLi yielded diiron anionic complexes 2 and 3, respectively, featuring a short Fe-Fe interaction supported by three bridging phosphido groups and one additional terminal R₂P^- ligand at each iron center. Further tuning of the P-substrates bulkiness gave a neutral phosphido complex 4 possessing a tetrahedral Fe₄ cluster core held together by six bridging iPr₂P moieties. Moreover, we also describe the first homoleptic phosphanylphosphido iron complex 5, which features an iron center with low coordination provided by three tBu₂P-P(SiMe₃)^- ligands. The structures of compounds 1-5 were determined by single-crystal X-ray diffraction and 1-3 by ¹H NMR spectroscopy. Moreover, the electronic structures of 1-3 were interrogated using zero-field Mössbauer spectroscopy and DFT methods.

Versatile Coordination Chemistry of Hexa-tert-butyl-octaphosphine

The octaphosphine {cyclo-(P₄^tBu₃)}₂ (1) possesses a multifaceted coordination chemistry. The predominant binding mode is a P,P-chelate, e.g., in the monometallic chelate complex [MLL'(1-κ²P²,P^4')] in which the ligand 1 adopts a gauche conformation. Examples include square-planar (M = Rh^I, L = CO, L' = Cl (2), M = Pd^II, L = L' = Cl (3), M = Pt^II, L = L' = Cl (9)), tetrahedral (M = Co^-I, L = NO, L' = CO (4)), and trigonal-planar complexes [ML(1-κ²P²,P^4')] (M = Pd⁰, L = PPh₃, (5), M = Cu^I, L = Br (6)). With 2 equiv of [CuBr(SMe₂)], a dinuclear complex [(CuBr)₂(1-κ²P²,P^2',κ²P⁴,P^4')] (7) was obtained which features a synperiplanar conformation of the octaphosphine. A second coordination mode was also observed in [PtCl₂(1-κ²P¹,P^2')] (10) in which the bridge phosphorus atom in octaphosphine 1 is involved in the chelation, with the ligand in an antiperiplanar conformation. Thermolysis of selected complexes showed them to be suitable candidates for the generation of phosphorus-rich metal phosphides MP_x (x > 1).

Unexpected Isomerization of Hexa-tert-butyl-octaphosphane

Octaphosphane {cyclo-(P₄ tBu₃ )}₂ (1) undergoes an unexpected isomerization reaction to the constitutional isomer 2,2',2'',2''',3,3'-hexa-tert-butyl-bicyclo[3.3.0]octaphosphane (2) in the presence of Lewis acidic metal salts. The mechanism of this reaction is discussed and elucidated with DFT calculations. The results underline the fascinating similarity between phosphorus-rich and isolobal carbon compounds. The new bicyclic octaphosphane 2 shows a dynamic behavior in solution and reacts with [AuCl(tht)] (tht=tetrahydrothiophene) to give a mono- ([AuCl(2-κP³ )], 3) and a dinuclear complex ([(AuCl)₂ (2-κP³ ,κP^3' )], 4). With cis-[PdCl₂ (cod)] (cod=1,5-cyclooctadiene), the chelate complex ([PdCl₂ (2-κ² P² ,P^2' )], 5) with a different coordination mode of the ligand was obtained.

An unusual Ni2Si2P8 cluster formed by complexation and thermolysis

A ternary Ni₂Si₂P₈ cluster compound is formed selectively by thermolysis of a well-defined nickel complex. This reaction illustrates a potentially useful strategy for the preparation of heteroatom-doped transition metal-phosphide clusters.

Making and breaking of phosphorus–phosphorus bonds

In contrast to their mostly unstable isolobal carbon counterparts, oligophosphanide anions, such as M(cyclo-P5tBu4) (M=Li, Na) and M2(P4R4) [M=Na, K; R=Ph, tBu, 2,4,6-Me3C6H2 (Mes)], have unique features, depending on their composition and structure, and are highly suitable building blocks for the synthesis of phosphorus-rich metal compounds. However, alkali metal oligophosphanediides are highly reactive and highly reducing, and a major problem is their tendency for disproportionation in reactions with electrophiles. This, however, can also give rise to a fascinating chemistry of making and breaking of P–P bonds. On the other hand, neutral cyclooligophosphines, such as cyclo-(P5Ph5), are suitable stable ligands for the formation of phosphorus-rich metal complexes.

Group 6 metal carbonyl complexes of cyclo-(P5Ph5)

Group 6 metal (Cr, Mo, W) carbonyl complexes react with cyclo-(P5Ph5) to afford the phosphorus-rich complexes [Cr(CO)5{cyclo-(P5Ph5)-κP 1}] (1), [{Cr(CO)5}2{μ-cyclo-(P5Ph5)-κP 1,P 3}] (2), [M(CO)4{cyclo-(P5Ph5)-κP 1,P 3}] (with M=Cr (3), Mo (4), W (exo-5, endo -5)) depending on the reaction conditions. Complexes 1–5 were characterised by 31P{1H} NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. The cyclopentaphosphane remains intact and acts as monodentate (1), bridging (2) or bidentate (3–5) ligand. Compounds exo-5 and endo -5 are configurational isomers and essentially differ in the orientations adopted by the phenyl rings attached to the uncoordinated phosphorus atoms. The 31P{1H} NMR spectra show five multiplets for an ABCDE spin system. Theoretical calculations showed that exo-5 and endo-5 are practically isoenergetic, which is in good agreement with the observed equilibrium in solution between exo-5 and endo-5. The thermal properties of the complexes have also been evaluated.