Structural and bonding aspects of molybdenum tricarbonyl complexes of 2,4,6-tritertiarybutyl-1,3,5-triphosphabenzene, P3C3But3 and some λ3,λ3,λ5- and λ3,λ5,λ5-alkylated derivatives

Abstract

In contrast to the extensive organometallic chemistry of 1-phosphabenzenes (phosphinines) summarised by Le Floch [1] and others [2,3], the exploration of the behaviour of the corresponding 1,3,5-triphosphabenzene ring systems is much less developed. We described previously several h 1complexes of P 3 C 3 Bu t 3 with square-planar Pt(II) fragments [4] and Binger et al. reported the first examples of h 6 -ligated compounds typified by [M(CO) 3 (h 6 -P 3 C 3 Bu t 3)] (M = Mo, W), [Mn(h 5 -C 5 H 5 )(h 6 -P 3 C 3 Bu t3 )] and [Ru(h 4 -COD)(h 6 -P 3 C 3 Bu t3 )], (obtained directly from P 3 C 3 Bu t 3 ), which were not, however, structurally characterised [5]. Subsequently, Jones and coworkers [6] extended the range of h 6 -complexes to include [Ru(h 5 -C 5 Me 5 )(h 6 -P 3 C 3 Bu t3 )][PF 6 ] and [Rh(h 4 -COD) (h 6 -P 3 C 3 Bu t3 )][BAr f 4 ], whose structures were established by single-crystal X-ray diffraction studies.Elsewhere [7], we have structurally characterised the remarkable triple-decker compound [{Sc(P 3 C 2 Bu t 2 )} 2 -m-(h 6 -P 3 C 3 Bu t3 )] in which the 1,3,5-triphosphabenzene ring bridges two scandium(I) centres. Furthermore, in unpublished work, we have synthesised and fully structurally characterised the first simple sandwich compounds [M(h 6 -P 3 C 3 Bu t 3 ) 2 ] (M = Zr, Hf) containing these ring systems, (albeit in very low yield), by metal-vapour syntheses directly from the phosphaalkyne, t BuCP [8].Photoelectron spectroscopic studies and DFT calculations showed that the 1,3,5-triphospharene complexes [M(CO) 3 (h 6 -P 3 C 3 Bu t3 )] (M = Cr, Mo, W) have a higher first IE compared with their corresponding carbocyclic counterparts [M(CO) 3 (h 6 -C 6 H 3 Bu t3 )]. An electronic structure analysis indicated significantly stronger bonding in the former complexes as a result of the greater metal-ligand back donation to lower lying LUMOs of the phosphorus substituted ring [9].Complexation of phosphinines is related to the aromaticity of these compounds, which is comparable to that of benzene [10,11]. Accordingly h 6 -complexation of phos-

Cationic Gold(I) Complexes of 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene

“…Computational studies on TPB have previously been conducted, but none directly tackling the aromaticity of η 1 metal complexes. 6,23,24 Pleasingly, the optimized structures for both 1 and 2 reproduce the salient features of the solid-state structures. Aromaticity was assessed using nucleus-independent chemical shifts (NICS-1) 25 which measure the absolute chemical shielding of ghost atoms placed 1 Å above the centers of the target rings.…”

“…One key goal was oligomerization of phosphaalkynes, 2 on account of the parallels to the development of the synthetic chemistry of the acetylene cyclooligomers, and a particularly striking subset of these reactions was cyclotrimerization to yield 2,4,6-tri-tert-butyl-1,3,5-triphosphosphabenzene, which is not only a challenging synthetic target but also raises important questions regarding heteroaromaticity. 3−5 The coordination chemistry of this species was evidently of interest, as it can bind not only in a π fashion characteristic of arene−metal interactions but in addition the lone pair on each P center could be utilized for metal binding: This dual binding mode is demonstrated in the work of Tate et al 6 Several crystallographically characterized examples of η 6 -2,4,6-tri-tert-butyl-1,3,5-triphosphosphabenzene (TPB) complexes of transition metals have been reported, 7,8 but only a solitary example of η 1 bonding, that of a Pt(II) complex which was structurally characterized by multinuclear NMR spectroscopy. 9 In addition, we note the reactions of weakly coordinating anion sources of the electrophiles H + , CH 3 + , and [R 3 Si] + , which have been shown to add to TPB at a P center.…”

2,4,6‐Tri(hydroxy)‐1,3,5‐triphosphinine, P3C3(OH)3: The Phosphorus Analogue of Cyanuric Acid

“…The P 3 C 3 unit in 7 and 8 is again planar and binds to the molybdenum center in a η 6 ‐coordination mode. The average P−C bond distances (1.765 and 1.768 Å) are slightly but significantly elongated compared to those in 4 also with respect to the Mo(CO) 3 ‐coordinated P 3 C 3 ( t Bu) 3 (1.753 Å) . The endocyclic P‐C‐P angles in 7 and 8 are somewhat widened and the C‐P‐C angles slightly narrowed with respect to 4 .…”

Synthesis of Chalcogenidoimidodiphosphinato–RhI Complexes and DFT Investigation of Their Catalytic Activation in Olefin Hydroformylation

“…Therefore, the RhS 2 P 2 N metallocycle is not planar and adopts a slightly distorted boat conformation, with the S1 and P2 atoms occupying the apices. It should be noted that compounds containing σ 4 ,λ 5 ‐phosphorus atoms can be nonplanar and still exhibit delocalization of the π‐electron density 65–67. The magnitude of the average Rh–S bond lengths (2.389 Å) and the S1–Rh–S2 angle (98.3°) is typical of similar complexes in which ( R L– S , S′ ) – ligands form six‐membered rings and adopt the boat conformation 6,68.…”