The five‐coordinate geometry is an important factor in phosphoryl group transfer, particularly for phosphate ester hydrolysis. In the following review we analyze the five‐coordinate geometries for a range of VO4X coordination spheres with regard to their structure from the point of view of square pyramidal or trigonal bipyramidal geometries. The actual differences for the coordination environment of the reported small molecule structures are compared to the coordination environment of vanadate complexed to a protein tyrosine phosphatase (PTP) with four coordinating O atoms and one S atom. These considerations demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated. This analysis suggests that it is a combination of structural and electronic properties leading to the perfect combination of reactivity and stability for the potent protein phosphatase inhibitor complex, thus confirming the fact that some other geometries have been reported.

We report intramolecular proton transfer reactions to functionalize carbon monoxide and tert‐butyl nitrile from a bis(phosphido) thorium complex. The reaction of (C5Me5)2Th[PH(Mes)]2, Mes=2,4,6‐Me3C6H2, with 1 atm of CO yields (C5Me5)2Th(κ2‐(O,O)‐OCH2PMes‐C(O)PMes), in which one CO molecule is inserted into each thorium–phosphorus bond. Concomitant transfer of two protons, formerly coordinated to phosphorus, are now bound to one of the carbon atoms from one of the inserted CO molecules. DFT calculations were employed to determine the lowest energy pathway. With tert‐butyl nitrile, tBuCN, only one nitrile inserts into a thorium–phosphorus bond, but the proton is transferred to nitrogen with one phosphido remaining unperturbed affording (C5Me5)2Th[PH(Mes)][κ2‐(P,N)‐N(H)C(CMe3)P(Mes)]. Surprisingly, reaction of this compound with KN(SiMe3)2 removes the proton bound to nitrogen, not phosphorus.

New triple-decker complexes with bridging tetramethylcyclopentadienyl ligands were synthesized by the reaction of electrophilic metal fragments with octamethylferrocene, Cp′2Fe (Cp′ = C5Me4H). The reaction of coordinatively unsaturated ruthenium cations [(C5R5)Ru]+ (R = H, CH3) with Cp′2Fe afforded purple-colored heterometallic triple-decker complexes [(C5R5)Ru(μ-Cp′)FeCp′]+ by direct electrophilic addition. Surprisingly, the analogous reaction with the coordinatively unsaturated manganese cation [Mn(CO)3]+ and Cp′2Fe produced a blue homometallic triple-decker complex, [Cp′Fe(μ-Cp′)FeCp′]+, by ring abstraction and subsequent addition of the newly generated cation [Cp′Fe]+ to an equivalent of Cp′2Fe. Three air-stable triple-decker complexes, [Cp′Fe(μ-Cp′)FeCp′]+ (2), [CpRu(μ-Cp′)FeCp′]+ (3), and [Cp*Ru(μ-Cp′)FeCp′]+ (4), have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

A study of the comparative reactivity of CO, CO2, tBuCN, and tBuNC with (C5Me5)2An­[P­(H)­Mes]2 (An = Th, U) has been undertaken. While CO2 and tBuNC form identical products with both metals, namely (C5Me5)2An­[κ2(O,O)-O2CPH­(Mes)]2 and (C5Me5)2An­[η2(tBuNCPMes]­(CNtBu), respectively, differing results are obtained with CO and tBuCN. The reaction of tert-butylnitrile with (C5Me5)2U­[P­(H)­Mes]2 in a 2:1 ratio leads to double insertion into the U–P bonds and elimination of H2PMes, forming the diketimido complex (C5Me5)2U­[κ2(N,N)-(NCtBu)2P­(Mes)]. This is a case in which the analogous reaction with (C5Me5)2Th­[P­(H)­Mes]2 affords a different product, (C5Me5)2Th­[PH­(Mes)]­[κ2(P,N)-N­(H)­C­(CMe3)­P­(Mes)]. The reaction of 1 atm of CO with (C5Me5)2U­[P­(H)­Mes]2 results in double insertion with proton migration from one phosphido ligand to one of the CO carbons to form (C5Me5)2U­[(κ2(O,O)-OCPMesC­(O)­(H)­P­(H)­Mes]. This is in contrast to the previously published result of the reaction between (C5Me5)2Th­[P­(H)­Mes]2 and CO, in which the product is similar, but both protons from the phosphido ligands migrate to one carbon atom, resulting in (C5Me5)2Th­[κ2(O,O)-OC­(H)2P­(Mes)­C­(O)­P­(Mes)]. Density functional theory calculations demonstrate that the mechanisms are quite similar and therefore a similar product is formed, except uranium is less acidic, and the final C–H bond formation does not occur.