Relative strength of 4d vs 5d .delta.-bonds: rotational barriers of isostructural molybdenum and tungsten porphyrin dimers

Collman, James P.; Garner, James M.; Hembre, Robert T.; Ha, Yunkyoung

doi:10.1021/ja00030a026

Cited by 37 publications

(25 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Collman and co-workers [707][708][709] have pioneered the study of rotations in dimeric metal-porphyrin complexes which involve a formal metal-metal quadruple bond. 710,711 In their seminal paper, 707 they measured the barriers to rotation in three different binuclear molybdenum(II) porphyrins (178)(179)(180) using DNMR and found them to be identical within experimental error (∼10 kcal mol -1 ).…”

Section: Bisporphyrinato and Related Complexesmentioning

confidence: 99%

Artificial Molecular Rotors

et al. 2005

View full text Add to dashboard Cite

Section: Bisporphyrinato and Related Complexesmentioning

confidence: 99%

Artificial Molecular Rotors

et al. 2005

View full text Add to dashboard Cite

“…[10][11][12][13] In all cases the results have been in the range of 10-13 kcal mol -1 . The "barrier to rotation" measured in this way is the difference in free energy between the most stable rotational conformation (not necessarily of D 4h symmetry but probably close) and the least stable one (not necessarily of D 4d symmetry, but probably close).…”

Section: Internal Rotationmentioning

confidence: 99%

Physical, Spectroscopic and Theoretical Results

Cotton

2005

Multiple Bonds Between Metal Atoms

View full text Add to dashboard Cite

Structural Correlations Bond orders and bond lengthsThroughout the preceding chapters of this book we have reported and in some cases discussed the lengths of the multiple bonds between metal atoms. We have reported in tabular form most of the M-M distances that have been determined crystallographically. It is now time to make some general comments on these distances in relation to our understanding of the M-M bonds.It is a general qualitative rule in chemistry that bond lengths and bond orders are inversely related. In some limited areas, particularly with the fi rst-row elements carbon, nitrogen, and oxygen, quantitative relationships expressing bond length as a single-valued function of bond order are well known. However, these quantitative relationships are based heavily on faith, as well as fact. Bond lengths are facts; bond orders are not. In the process of inferring a bond order from a bond length one is often getting out no more than what was put in to begin with.We shall not further digress into a discussion of the philosophical ambiguities of these quantitative bond order-bond length correlations because they have proven to be useful, within their own sphere of application. However, there is no a priori reason to expect that similar procedures will (or will not!) work in the very different realm of metal-to-metal bonds. Experience is the only test, and experience thus far has shown that M-M bonds cannot usefully be treated in such a way.In the realm of M-M bonds it is best to invoke only a qualitative inverse relationship between bond order and bond length and to defi ne bond order only in a qualitative or ordinal way. In this book we have used the term M-M bond order only to indicate how many electron pairs are believed, on the basis of essentially qualitative considerations, to play a signifi cant part in holding the pair of metal atoms together. We condemn as foolish and hopeless any effort to associate a unique, precise, quantitative bond order with each and every M-M internuclear distance.In principle, M-M bond lengths, like others, should be amenable to treatment by the method of molecular mechanics, and some efforts [1][2][3][4] (hampered by a dearth of necessary experimental data) to do this have been reported. In general the results are encouraging and can account for

show abstract

“…334 This provides a caveat regarding the potential for unexpected intermediates and the real need to consider other modes of binding when considering bidentate chelates. Biphep, BINAP, and similar ligands, for example, have shown bidentate binding modes that involve P ,C rather Table 2 Leading references for additional selected topics on stereochemically nonrigid molecules Metal -metal multiple bond hindered rotation [335][336][337] Ligand lone pair inversion Phosphide inversion…”

Section: 1319-24306310mentioning

confidence: 99%

Stereochemical Nonrigidity of Organometallic Complexes

Faller¹

2005

Encyclopedia of Inorganic Chemistry

View full text Add to dashboard Cite

Compounds that undergo intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges are described as stereochemically nonrigid. Analysis of 1D and 2D NMR spectra as a function of temperature often allow the rates, as well as the mechanisms of interconversion of conformers or isomers, to be determined. Examples were selected to illustrate the importance of stereochemical nonrigidity in reactivity and the potential for affecting stereochemistry in the products of reactions.

show abstract

Relative strength of 4d vs 5d .delta.-bonds: rotational barriers of isostructural molybdenum and tungsten porphyrin dimers

Cited by 37 publications

References 0 publications

Artificial Molecular Rotors

Artificial Molecular Rotors

Physical, Spectroscopic and Theoretical Results

Stereochemical Nonrigidity of Organometallic Complexes

Contact Info

Product

Resources

About