(Cyclobutadiene)iron TricarbonylA Case of Theory before Experiment

Reductive assembly of cyclobutadienyl and diphosphacyclobutadienyl rings at uranium

“…HOMO-6 (477a) and HOMO-7 (476a) involve uranium-cyclobutadienyl combinations that are of p-character and employ c 3 and c 2 cyclobutadienyl p-orbital combinations (Fig. 6), respectively, which are usually invoked in the molecular orbital descriptions of the bonding between transition metal centres and cyclobutadienyl 5 . However, for 3, the notable difference is that the uranium 5f-orbitals are almost exclusively employed, whereas transition metals typically employ p-and d-orbital combinations.…”

“…These ligands, together with allyl and alkene ligands, constitute the important class of p-bound organometallic ligands that have proven instrumental in the development of d-orbital bonding theory. The strategy of using metals to construct and stabilize reactive p-systems has met with much success, for example, affording otherwise inaccessible organic groups, such as the square, rather than rectangular form of cyclobutadiene 5 . Furthermore, metal p-complexes find numerous applications in organic synthesis and catalysis, where complexation of a metal can increase or invert the reactivity of p-systems [6][7][8] .…”

A Phosphorus Analogue of Bis(η4‐cyclobutadiene)iron(0)

“…On a preparative scale, 3 was generated by oxidizing K 2 with [Cp 2 Fe][PF 6 ] to give, upon isolation, deep red crystals that are highly soluble in hydrocarbon solvents. The X-ray crystal structure of neutral, 16-electron 3 ( Figure 5) revealed a C 2 -symmetric sandwich structure akin to anion 2.…”

“…Future studies will focus on a more detailed characterization of the iron oxidation state in 1-3 and the influence of metal coordination on the magnetic and redox properties of these compounds. [22] Experimental Section K 2: tBuCP (5 mL, 10.0 mmol, 2 m solution in hexanes) was added dropwise to a deep brown solution of [K( [18] 6 ] (0.050 g, 0.15 mmol) was added to a dark orange solution of K 2 (0.106 g, 0.14 mmol) in THF (6 mL), and the mixture was stirred at room temperature overnight. The solvent was removed completely, the ferrocene byproduct was removed by sublimation (10 À2 torr, 50 8C), and the dark residue was extracted into n-pentane (10 mL).…”

Gold(I) and Silver(I) Complexes of Diphosphacyclobutadiene Cobaltate Sandwich Anions

“…[3] The cyclodimerization of phosphaalkynes R À C P in the coordination sphere of a transition-metal atom is an elegant method for the preparation of metal-coordinated diphosphacyclobutadienes. [1,4] The formation of the 1,2-diphosphacyclobutadienes through head-to-head dimerization is observed with small substituents on the phosphaalkyne, for example, R = Me, whereas bulkier substituents favor the formation of 1,3-diphosphacyclobutadienes through head-totail dimerization. [5] 1,3-diphosphacyclobutadiene complexes of type A were first prepared independently by the groups of Regitz, Binger, and Nixon in 1986 through the reaction of ethene complexes [(C 5 R' 5 )MA C H T U N G T R E N N U N G (h 2 -C 2 H 4 ) 2 ] (M= Co, Rh, Ir, R' = H, Me) with tert-butylphosphaalkyne (tBu-CP).…”