Tripod metal entities tripodM are sterically congested systems. The conformations adopted by compounds CH3C(CH2PPh2)3–n[CH2P(oTol)2]nMo(CO)3 (n = 1: 1, n = 2: 2, n = 3: 3) will thus be largely determined by the repulsive forces acting in these molecules. The steric demand of the o-tolyl groups impedes their free rotation and enantiomerization processes referring to the compounds as a whole are sufficiently slow to permit their analysis by NMR techniques. Through a combination of line-shape analysis, EXSY methods, and coalescence experiments, the ΔG‡ values for these conformational enantiomerization processes have been determined as ΔG‡298K = 54.3, 57.9, 65.5 kJ·mol–1 for compounds 1, 2, and 3, respectively. By an exhaustive search on a force field generated hypersurface, activation energies of 53, 57 and 69 kJ·mol–1 have been calculated. Thus, the force field approach correctly reproduces the dependence of the activation energy on the degree of o-tolyl substitution. Moreover, the force field simulation also gives an insight into the individual microsteps of the enantiomerization pathways.

Starting from 4-methoxybenzylmalonic ester MeOC6H4CH2CH(COOEt)2, the synthesis of the tripod-ligand HOC6H4CH2C(CH2PPh2)3, 12, functionalized with a phenolic group at its backbone, is achieved in a few steps. Ether derivatives of 12 show the normal coordination behavior of RC(CH2PPh2)3. Thus MeOC6H4CH2C(CH2PPh2)3 forms the complexes [7·Fe(NCMe)3] (BF4)2 (8) and 7·Mo(CO)3 (9). The phenolate derived from 12 by deprotonation reacts with the CH2Cl groups of Merrifield resin to form covalently polymer fixed 12 with high efficiency. The polymer bound tripod ligands undergo tripod typical coordination reactions. In addition to the usual spectroscopic and analytical techniques, X-ray analyses of derivatives of 12 as well as of 8 and 9 are used to identify the products.

Neopentane-derived tripod ligands of the general type HOCH2C(CH2PPh2)(CH2Y)(CH(2)Z) (1; Y, Z = PPh2, SR) are notoriously resistant to ether formation at their hydroxy group. Two routes have been found, which allow the transformation of 1 into ether functionalized tripod ligands ROCH2C(CH2PPh2)(CH2Y)(CH(2)Z) (Y = Z = PPh2: 5, Y = Z = SR: 8). One of these strategies relies upon the eta 3 coordination of 1 in 1 . Mo(CO)(3) (2). By this way the donor groups are efficiently protected and the steric encumbrance of the CH2OH group at the backbone of the ligands is greatly reduced by fixing three arms of the neopentane scaffolding to the metal center. After deprotonation, reaction with electrophiles will produce the corresponding ether derivatives ROCH2C(CH2PPh2) (CH(2)Z)(2) (3). Mesylation of 2 leads to MeSO2OCH2C(CH2PPh2)(3). Mo(CO)(3) (4), which reacts with alkoxides to produce 3 in a sequence of reversed polarity. Ligands 5 [ROCH2C(CH2PPh2)(3)] are liberated from 3 by UV irridation of their solutions in the presence of pyridine N-oxide. Direct etherification of 1 is also possible in some cases after deprotonation of 1 by KOtBu and subsequent reaction with an electrophile RX in the narrow temperature range between -10 and +20 degrees C. By this way, omega-methyl polyglycol ether functions are easily introduced resulting in H3C(OC2H4)(n)OCH2C(CH2PPh2)(3) (5g, h).

Weak antiferromagnetic exchange interactions are observed in two Co-II dimers of the general formula [{(triphos)Co}(2)(mu-dicarboxylato)](BF4)(2) where the dicarboxylate is the dianion of fumaric acid [3.(BF4)(2)] or terephthalic acid [4.(BF4)(2)] and triphos is the tridentate phosphorus ligand 1,1,1-tris(diphenylphosphanomethyl)ethane. In these complexes the metal ions are separated by 8 and 10 Angstrom, as determined by X-ray crystallography. Insight into the interaction pathway is gained through molecular orbital calculations performed on model compounds. The influence of bridging-ligand distortions and the stereochemistry around the two cobalt centres is discussed.

Hexadentate dinucleating ligands that are based on a bridging pyrazolate bearing chelating side arms [3,5-(R2NCH2)(2)C3N2H2; R2N = Me2N(CH2)(3)NMe (HL1), Me2N(CH2)(2)NMe (HL2)] reacted with NiCl2 . 6H(2)O to yield complexes ClNi(mu-Cl)(mu-L-1)NiCl 1 ((Ni2LCl3)-Cl-1) and ClNi(mu-Cl)(mu-L-2)NiCl 2 ((Ni2LCl3)-Cl-2), respectively. Depending on the side-arm chain length and the solvent used for crystallisation these complexes either crystallised as dicrete bimetallic units (1) or were assembled via di-mu-chloro linkages to form a tetranuclear compound [ClNi(mu-Cl)-(mu-L-2)Ni(mu-Cl)(2)Ni(mu-Cl)(mu-L-2)NiCl] 2a ([(Ni2LCl3)-Cl-2](infinity)) or a novel bridge-alternating one-dimensional chain [Ni(mu-Cl)(mu-L-1)Ni(mu-Cl)(2)](infinity) 2b ([(Ni2LCl3)-Cl-2](infinity)) in the solid state. Variable-temperature magnetic susceptibility measurements revealed antiferromagnetic coupling within the basic mu-chloro-mu-pyrazolato bridged bimetallic framework in all cases and also suggested antiferromagnetic superexchange propagated by the di-mu-chloro linkage in 2b. The latter result is rationalised on the basis of the specific geometric findings for this di-mu-chloro linkage, in particular the unusually large Ni-Cl-Ni angle [101.37(4)degrees].

Reaction of tripod cobalt(II) templates [{CH3C(CH2PAr2)(3)}Co-II] with potentially bridging ligands L generates the dinuclear compounds [(tripod)-Co-L-Co(tripod)](2+). With L = oxalate (C2O42-) a biscobalt(II) complex (1) is Formed, while with L = C6H2O42-, the dianion derived from 2,5-dihydroxy-1,4-benzoquinone (anilic acid), two-electron transfer within the dimetallic unit occurs and a biscobalt(III) charge distribution results (2a), as shown by X-ray structural analyses of 1 and 2 a, NMR spectroscopy, and theoretical investigations by the INDO method, Complex 2a exhibits an unusually intense, low-energy absorption in its electronic spectrum; this is explained with a simple MO model. One-electron reduction of 2 a generates the corresponding mixed-valence complex, which is highly stabilised through extensive electron delocalisation. Substituents at the 3,6 posi tions of the bridging ligand (Cl, Br, I, NO2, Me, iPr. Ph: 2b-h) as well as alkyl substitution at the aromatic rings of the tripod ligands (3,4) influence the optical and electrochemical properties consistent with the proposed model of charge distribution, Formal replacement of one [(tripod)Co-III](3+) moiety by [CH2](2+) leads to the mononuclear complex 6, which is shown to be a typical [(tripod)Co-III-catecholato)](+) complex, Therefore the substantially different optical and electrochemical properties of the dinuclear complexes with respect to those of 6 result from strong metal-metal interactions mediated by the bridging ligand.

Depending on the reaction conditions, different products are obtained from the reaction of CoCl2 with CH3C(CH2PPh2)(3) (triphos), including the law-spin complexes [(triphos)Co(mu-Cl)(2)Co(triphos)](2+) (1(2+)) and [(triphos)CoCl2] (3), their solid-state structures being determined by X-ray methods. In solution, additionally, a four-coordinate high-spin complex [(eta(2)-triphos)CoCl2] (2) is present, its concentration relative to that of 3 depending on the solvent and the temperature. The reactivity of these species toward Lewis acids is investigated leading to the novel heterodinuclear complexes [(triphos)Co(mu-Cl)(2)MCl2] (M = Fe (5), Co (6)). Reactions with Lewis bases L yield complexes of the rare type [(triphos)CoCl(L)](+) (L = CO (7(+)), PMe3 (8(+)), NH3 (9(+)), CH3CN (10(+))). One electron reduction of 3 leads to the previously prepared pseudotetrahedral [(triphos)(CoCl)-Cl-I] complex 11, and one-electron oxidation to the novel trigonal-bipyramidal low-spin complex [(triphos)(CoCl2)-Cl-III](+) (12(+)).