Synthesis and coordination chemistry of neutral phospha(iii)guanidines. Formation of 1-aza-3-phospha-4-metallacyclobut-1-ene rings at group 6 metalsElectronic supplementary information (ESI) available: an ORTEP representation and bond lengths and angles for 3a; crystal structure and refinement data, bond lengths and angles and an ORTEP representation of the molecular structure of Mo(CO)4(pip)2. See http://www.rsc.org/suppdata/dt/b3/b302554c/

Syntheses and Structures of [CH2(NCnH2n)2]Mo(CO)4 (n = 4,5) Complexes with Bis(cycloamine) Ligands Easily Prepared from CH2Cl2

“…Thermal ellipsoid plots and relevant bond distances are shown in Figure . Comparison of 2 , [CH 2 (pip) 2 ]­Mo­(CO) 4 , with the previously determined structure of 3 , cis -(pip) 2 Mo­(CO) 4 , shows the CH 2 (pip) 2 ligand to have a larger steric impact on the surrounding carbonyls leading to a distorted octahedral geometry (Figure ). With the amines tied back by the methylene group, a small bite angle of 62.55(14)° is observed and the six-membered rings adopt a conformation that points toward the metal center, compressing the equatorial carbonyls and giving a C(2)–Mo(1)–C(2)′ angle of 86.0(2)°.…”

“…View down the axial carbonyls of cis -(pip) 2 Mo­(CO) 4 , 3 (left), [CH 2 (pip) 2 ]­Mo­(CO) 4 , 2 (center), and [CH 2 (pyr) 2 ]­Mo­(CO) 4 , 1 (right). Capped stick representations with angles around the molybdenum center.…”

Coordination Chemistry of Isomeric Mixtures of Linked Di(phosphaguanidine) Compounds: A Spectroscopic and Crystallographic Study

“…During analysis of the phosphaguanidines, different arrangements of the N -substituents were noted, depending on the orientation of the imine bond and the relative position of the N H hydrogen atom (Figure ) . For example, data for the noncomplexed species were consistent with an E syn pattern in the solid and solution states, while the Z anti conformation is enforced upon chelation to a “M(CO) 4 ” fragment . More recently we have identified an equilibrium between the E syn and Z syn forms for the phospha(V)guanidines, Ph 2 P(E)C{NR}{NHR} (E = S, Se), postulated as arising from attractive E···H−N nonbonded interactions.…”

“…During the course of their development, the steric and electronic properties have been extensively modified, facilitated by the ease with which substituents possessing different physical and chemical properties can be incorporated at the phosphorus atom. We have recently developed a novel class of phosphine compound with general formula Ph 2 PC{NR}{NHR} (R = i Pr, Cy) (we refer to this class of compound as phospha(III)guanidines, by reference to its relationship to conventional tetrasubstituted guanidines of general formula R‘ 2 NC{NR}{NHR}), featuring a C -bound amidine unit, and reported different coordination behavior including anionic [ N , N ‘ ] - and [ N , P ] - and neutral P - and N , P -coordination and a bridging mode between different metal centers…”

“…The predominant conformation for the amidine unit in 3a is Z anti , indicating a change in the energy profile of the different substituent positions compared with the proligand. However, the presence of a broad doublet centered at δ 5.32 in 3a is characteristic of an N H resonance from an E syn amidine, suggesting that the asymmetric species corresponds to the { Z anti : E syn } isomer. This diastereoisomer is in exchange with one of the symmetrical species (but not the other), which we therefore assign as the corresponding { Z anti : Z anti }.…”