DG Note 27-3

DG Note 27412Van Wazer Structural Reorganization

A review (which was originally drafted in 1975) of ideas generated from my participation in JR Van Wazerrsquos lsquoStructural- Reorganization-Throughout-The-Periodic-Tablersquo research program (which had been offered but not published or otherwise put to use) is now re-formatted below

---------------------------------------------------------------------------------------- SCRAMBLING REACTIONS

David Grant BSc PhD

During the latter part of the eighteenth century Berthollet and Proust debated the constancy of the combining proportions of elements in chemical species (1) Berthollet recognized the importance of equilibria regarding constant proportions as being the exception There is a grain of truth in this eg polymeric and amorphous species can exhibit variable compositions and while numerous compounds including those based on carbon backbones have a high probability of remaining unchanged for a long time some substances having central atoms other than carbon at structural centers are intrinsically of lower stability than are purely organic molecular species This applies to the liquid phase which can facilitate rapid molecular rearrangements to occur (and most especially if this process is fast with respect to the time required to separate the individual molecular species then the scrambled product is what is most commonly encountered) This scrambling may however not be detected by vibrational spectroscopy or by X-ray diffraction Numerous reaction products previously though to be single compounds have been found to be the scrambled mixtures which if at equilibrium will exhibit some reproducible physical properties in a manner similar to that of pure compounds

The most general form of scrambling was established by Van Wazer (2) (ca 1955) who extended the earlier concepts of Flory and demonstrated that equilibria of which the following is typical are established

(RO)2gtP(O)(OR) (neso) + -Ofrac12-P(O)(OR)-Ofrac12- (middles) harr 2 Ofrac12-P(O)lt(OR)2 (ends)

(further equilbria are usually measured to distinguish the middles in rings from those in chains and the ends on long chains from those on short chains In the phosphate-condensed phosphate systems branch groups also take part in equilibria like ends + branches 2 middles)

The Van Wazer method of characterization of chemical systems is useful for the elucidation of the products of synthetic organometallic chemistry where conventional lsquoorganic chemical logicrsquo fails to properly identify the substances formed in any attempted stepwise synthesis of an inorganic molecular structure or a mixed inorganic-organic element (eg B P As Si etc) - containing derivative An example of former situation arose is an attempt to synthesize an ldquoisotetraphosphaterdquo structure While a composition which appeared to contain this structure as suggested by some physical measurements etc seemed to have been produced a later re-evaluation by NMR showed that this structure if formed initially had completely rearranged to produce a reproducible mixture the composition of which could be exactly predicted using the scrambling equilibrium hypothesis suggested by Van Wazer (3) Such rationalizations were similarly useful for arriving at the correct chemical constitution of a product arising from attempts to prepare octamethyltetraminopyrophosphate (((CH3)2N)2P(O))2O) (OMPA) (cf 3a) (the reaction product however showed the NMR spectrum of a completely scrambled mixture of the same stoichiometry A similarly completely scrambled mixture also apparently arose from attempts to prepared specific polysilicate esters eg RO-(Si(OR)2-(O-Si(OR)2)n-O-Si(OR)2-OR (where R is an organic group)

Scrambling was first recognized as an important phenomenon in tetra-coordinate Pb chemistry by Callingaert and Beatty in 1939 (4)

Ethyl vs methyl groups were found to scramble near-randomly on Pb and some other metal centers

Flory (5) considered that an equilbrium

middles + ends middlesacute + endsacute

occurred between groups in polyester chains Forbes and Anderson

observed the random sorting of Cl vs Br on ndashClt (6) and on other centers

Many cases for a wide range of ligands and centers are now known to exhibit scrambling behavior Classification into near-random or highly non-random systems is often helpful Many systems are near-

random eg halogen exchange on

-V(O)lt (7)

-P(O)lt (8 )

Ti (6 co-ord) (9)

-Hg- (2 co-ord) (10)

gtGelt (4 co-ord) (11)

gtSnlt (4 co-ord) (12)

gtSilt (4 co-ord) (13)

-Blt (3 co-ord) (14)

[and also eg RnMX4-n (R = alkyl etc X = halogen M = Ge Sn Si etc)]

Recent interest has been shown in CO exchange in cluster compounds (15) different sites may exhibit markedly different exchange rates Cf Fe3 (CO)12 scrambling (15a)

Examples of scrambling in polymer systems are in polysiloxanes (16) -silicates (17) -sulphates (18) -sulphones (19) -sulphides (20) -selenides (20) -borates (21) -phosphates (22) -phosphonates (23) -ethane oxydiphosphonates (24) -arsenites (25) -germthioxanes (26) -(fluoro)arsenious methylimides (27) and -tin sulphides (28)

Scrambling (at ambient temperature) of alkoxyl vs Cl groups on -V(O)lt is some 107 time faster than on -P(O)lt but both systems are similarly random (19)

An example of scrambling on ndashV(O)lt (V(O)Cl3 (CH3)3Si-O-Si(CH3)3) is shown in Fig 1

Fig1 [R=2Si(V+2Si)]

The greater rates of scrambling on transition-metal centers may give rise to lsquofluxionalrsquo activity (rapid often intramolecular NMR-detected scrambling) (29) The use of transition-metal compounds as catalysts for organic reactions eg in hydrogenation isomerization and polymerization seems to be afforded by the scrambling potential at the metal eg scrambling-related polymer generation arises from the -olefin monomer additions to the metal-centered scrambling centers which are the active sites of the Ziegler-Natta polymerization catalysts In the polymer chain propagation process the transition-metal forms metal-carbon bonds into which -bonded olefinic bonds insert This is likely to be a reversible (equilibrium) reaction but is far displaced towards the polymer form at a polymerization temperature of ca 70oC (30) Whether isotactic or stereospecific polymers arise during this insertion process seems to be dependent on the rate of structural reorganization of metal bound co-ligands

A further example of organic reaction catalysis at metal centers is the metathesis of olefins at W and Mo centers which leads to an apparent scrambling of the alkyl groups about the double bond (31)

Scrambling may be catalyzed both positively or negatively eg phosphorus halides scrambling is accelerated by H2O (32) for boron halides scrambling is inhibited by bases (33)

There is probably no single type of mechanism which can explain scrambling reactions Under scrambling conditions a mechanistic approach to the rationalization of chemical reaction products obtained at sub-scrambling temperature so useful for organic reactions at near-ambient temperatures is much less helpful for achieving an understanding of scrambling process The important criteria are now knowledge of the equilibria(perhaps more accurately described as [enthalpy-entropy compensated] extrathermodynamic pseudoequilibria) which govern this behavior (34)

A general (first order approximation) principle of scrambling is that the type of equilibrium (eg random or non-random) is dependent on the ligands and is independent of the sites the rate of scrambling however depends on the site (35) Carbon is the slowest site Scrambling of hydrocarbons (eg at 1000oC) gives CH4 C2H6 C3H8 and char (closed system) Phosphorus hydrides behave similarly (lsquocharrsquo now being red phosphorus) as do silicon hydrides (36)

The outcome of high temperature scrambling behavior of hydrocarbons is derivable from the accurate thermodynamic data which is available for these compounds and the above scrambled corresponds to a thermodynamic equilibrium However at lower temperatures reversible exchange between aliphatic and aromatic carbon-based systems occurs These are likely to be pseudo-equilibria where the forward and reverse rates are not quite equal and proceed by different mechanisms this situation is illustrated by the scrambling of chlorocarbons in sealed-tubes where all chlorocarbons which have been studied give CCl4 C2Cl6 and C6Cl6 with inappreciable char formation (37)

The phenomenon of aromaticity may be considered to be a double bond scrambling around the ring Negative catalysis (Fe(CO)3 complexing sites) slow the process sufficiently for individual cyclohexatrienes to be distinguished (38)

In boranes and related compounds a variety of BHB

scrambling reactions have been reported eg with B3H8- (39)

Silicates scramble near-randomly (17) therefore giving rise to appreciable amounts of a large number of structures Nucleation of crystallization of a particular structure can remove it form the equilibrium eventually converting all of the molecules present[Bond exchange also can lead to flow in compositions beyond the gel point In inorganic polymers such as silicates bond exchange can lead to flow whereas flow in organic polymers flow most often involves the sliding of the intact molecules over each other]The formation of quite complicated structures in high yield in pre-biotic conditions could have been an outcome of scrambling reactions and subsequent nucleation of specific sub-types of molecules allowing the formation of specific lsquoproteinoidrsquo and poly-sugar-triphosphate molecules to be achieved in high yield

References

(1) Cf ldquo A Short History of Chemistryrdquo JR Partington Macmilllan London 1957 p 153

(2) ldquoPhosphorus and Its Compoundsrdquo Vol I JR Van Wazer Interscience New York 1959

CF Callis J R Van Wazer JN Schoolery and WA Anderson J Amer Chem Soc (1957)79 2719 JR Van Wazer CF Callis and JN Schoolery (1955) 77 4945

(3) E Schwarzman and JR Van Wazer J Amer Chem Soc (1960) 82 6009

(3a) cf eg JR Van Wazer Amer Scientist ref (36)

(4) G Caligingaert and HA Beatty J Amer Chem Soc (1939) 61 2748G Calingaert HA Beatty and HR Neal ibid (1939) 61 2755G Calingaert and H Soros ibid (1939) 61 2758G Calingaert HA Beatty and H Soroos ibid (1940) 62 1099

(5) PJ Flory J Amer Chem Soc (1942) 64 2205

(6) GS Forbes and HH Anderson J Amer Chem Soc (1944) 66 931

(7) RJH Clark and PD Mitchell JChem Soc Dalton 1972 2429

(8) LCD Groenwege and JH Payne Jr J Amer Chem Soc (1959) 81 6357

(9) PAW Dean and DF Evans J Chem Soc A 1970 2569

(10) M D Rausch and JR Van Wazer Inorg Chem (1964) 3761 Cf JC Lockart Chem Rev (1965) 65 131

(11) GM Burch and JRVan Wazer J Chem Soc A 1966 586 cf Inorg Chem 1964 3 268

(12) JJ Burke and PC Lauterbur J Amer Chem Soc (1961) 83 326 GS Forbes and HH Anderson ibid (1945) 67 1911 (1944) 66 931 G Calingaert H Soroos and V Hnizda ibid (1940) 62 1107 D Grant and JR Van Wazer J Organometal Chem (1965) 4

229

(13) K Moedritzer and JR Van Wazer Inorg Chem (1964) 3 268 and refs cited cf JR Van Wazer and K Moedritzer J Inorg Nucl Chem (1964) 24 73

(14) HK Hofmeister and JR Van Wazer J Inorg Nucl Chem (1964) 26 1209

MF Lappert MR Litzow et al J Chem Soc(A) 1971 383

(15) L Milone S Aime EW Randall and E Rosenberg JCS Chem Commun 1975 452 TJ Marks and GW Grynkewich J Organometallic Chem (1975) 91 C9-12 FA Cotton DL Hunter and P Lahuerti Inorg Chem (1975) 14 511(15a) BFG Johnson JCS Chem Commun 1976 703

(16) K Moedritzer and J R Van Wazer J Amer Chem Soc (1964) 86 802

(17) D Grant J Inorg Nucl Chem (1967) 29 69 RO Gould BM Lowe and NA MacGilp JCS Chem Commun 1974 720

(18) JR Van Wazer D Grant and CH Dungan J Amer Chem Soc (1965) 87 3333

(19) Unpublished work of D Grant and JR Van Wazer

(20) JR Van Wazer D Grant J Amer Chem Soc (1964) 86 3012

(22) JR Van Wazer CF Callis JN Shoolery and RC Jones J A Amer Chem Soc (1956) 78 5709 and 5715

CF Callis JR Van Wazer JN Shoolery and WA Anderson J Amer Chem Soc (1957) 79 2719 DP Ames S Ohashi CF Callis and JR Van Wazer ibid

(1959) 81 6350 M M Crutchfield CF Callis RR Irani and GC Roth Inorg Chem (1962) 1 813 LCD Groenweghe JH Payne and JR Van Wazer J Amer Chem Soc (1960) 82 5305 E Schwarzmann and JR Van Wazer ibid (1961) 83 365 DR Cooper and JA Semlyen Polymer (1972) 13 414 JR Van Wazer and S Norval J Amer Chem Soc (1966) 88 4415 LCD Groenweghe and JH Payne Jr J Amer Chem Soc (1959) 81 6357

(23) D Grant JR Van Wazer and CH Dungan J Polymer Sci (1967)A-15 57

(24) Unpublished work of D Grant (Glasgow University manuscript in preparation [(added later eventually published in Eur Polym J (1979) 15 1161)]

(25) JR Van Wazer K Moedritzer and DW Matula J Amer Chem Soc (1964) 86 807

(26) K Moedritzer and JR Van Wazer J Amer Chem Soc (1968) 90 1520

(27) MD Rausch JR Van Wazer and K Moedritzer J Amer Chem Soc (1964) 86 814

(28) K Moedritzer and JR Van Wazer Inorg Chem (1964) 3 943

(29) FA Cotton Chem Brit (1968) 4 345 Cf S Cradock EAV Ebsworth H Moretto and DWH Rankin JCS Dalton 1975 390 AJ Campbell CA Fyfe and E Maslowsky Jr Chem Commun 1971 1032 PC Angus and SR Stobart JCS Dalton 1973 2374

(30) Cf D Grant J Polymer Sci Polymer Letters (1975) 131

(31) Cf N Calderon and RN Hinrichs Chemtech (1974) 4 627 EL Muetterties and MA Busch JCS Chem Commun 1974 754 and refs cited AJ Amass Br Polymer J (1972) 4 327

(32) AD Jordan and RG Cavell Inorg Chem (1972) 11 564

(33) B Benton-Jones MEA Davidson JS Hartman JJ Klassen and JM Miller JCS Dalton 1972 2603 Cf MJ Bula JS Hartman and CV Raman ibid 1974 725

(34) DW Matula LCD Groenweghe and JR Van Wazer J Chem Phys (1964) 41 3105 RM Levy and JR Van Wazer ibid (1966) 45 1824 LCD Groenweghe JR Van Wazer and AW Dickenson Anal Chem (1964) 36 303 JR Van Wazer and K Moedritzer Angew Chem Internat Edit (1966) 5 341 K Moedritzer Inorg Chim Acta 1970 4 613 JR Van Wazer and LCD Groenweghe ldquoNuclear Magnetic Resonance in Chemistryrdquo B Pesce Ed (1965) 283 JR Van Wazer ldquoInorganic Polymer Chemistryrdquo J Macromol Sci 1967 A1 29 JC Lockart Chem Rev (1965) 65 131 Note added to ms later the Van Wazer scrambling phenomena are likely to be afforded by extrathermodynamic pseudoequilibria associated with enthalpy-entropy compensation phenomena the general occurrence of which throughout biology chemistry and physics putatively requires a re-think of classical thermodynamics eg involving reverse time and vacuum energy concepts ]

(35) JR Van Wazer Proc Conf Coord Chem 8th Vienna 1964 Springer-Verlag Vienna Ed V Gutman p162

(36) JR Van Wazer Amer Scientist (1962) 50 450

(37) NE Aubrey and JR Van Wazer J Amer Chem Soc (1964) 86 4380 D Grant J Appl Chem Biotechnol (1974) 24 49

(38) R Victor R Ben-Shoshan and S Sarel Chem Commun 1970 1680

(39) H Beall and CH Bushweller Chem Rev (1973) 73 465 cf EL Muetterties EL Hoel CG Salentine and MF Hawthorne Inorg Chem (1975) 14 950

Further References Scrambling Centre Indicated

JR Van Wazer et al J Inorg Nucl Chem (1964) 26 1209 (boron) Inorg Chem (1964) 3 139 (arsenic) J Amer Chem Soc (1964) 86 811 Inorg Chem (1964) 3 280 (phosphorus) Ibid (1965) 4 1294 (silicon) (silicon germanium) J Inorg Nucl Chem (1964) 26 737 (silicon) J Organometal Chem (1968) 12 69 (silicon) Ibid (1975) 85 41 ([silicon] phosphorus) Inorg Chim Acta (1967) 1 407 Ibid (1967) 1 (1967) 152 (silicon germanium) (cf K Moedritzer ibid (1971) 5 547 (1974) 10 163 (silicon germanium KM Abraham and JR Van Wazer J Inorg Nucl Chem (1975) 37 541 (silicon germanium) E Fluck JR Van Wazer and LCD Groenweghe J Amer Chem Soc (1959) 81 6363 (phosphorus) J Inorg Nucl Chem (1967) 291571 (germanium) Ibid (1964) 26 737 Ibid (1967) 29 1851 (silicon) Inorg Chem (1965) 4 1294 (review) J Chem Phys (1964) 41 3122 (several elements)

JG Reiss and SC Pace Inorg Chim Acta (1974) 9 61 (silicon)MW Grant and RH Prince J Chem Soc (A) 1969 1138 (silicon)(germanium)F Glocking SR Stobart and JJ Sweeney JCS Dalton 1973 2029 (mercury)AG Lee and GM Sheldrick ibid (A) 1969 1055 (thallium)JAS Howell and KC Moss ibid (A) 1971 2483 (tantalum)R Davis MNS Hill CE Holloway BFG Johnson and KH Al-Obaidi ibid (A) 1971 994 (molybdenum and tungsten)H Hagnauer GC Stocco and RS Tobias J Organometal Chem (1972) 46 179 (gold)CE Holloway J Coord Chem 19711 253 (tantalum)J Evans BFG Johnson J Lewis and JR Norton JCS Chem Commun 1973 807 (rhodium) JF Nixon B Wilkins and DA Clement JCS Dalton 1974 1993 (rhodium)J Evans BFG Johnson J Lewis and RWatt ibid 1974 2368 (rhodium)M Green and GJ Parker ibid 1974 333 (rhodium and iridium)AJP Domingos BFG Johnson and J Lewis ibid 1974 145 (ruthenium)TH Whitesides and RA Budnik JCS Chem Commun 1974 302

(ruthenium)F Calderazzo M Pasquali and T Salvatori JCS Dalton 1974 1102 (uranium)RJ Cross and NH Tennent ibid 1974 1444 (platinium)T Mole Organometal Reactions (1970)11 (review aluminum)NS Ham and T Mole Progr Nuclear Magnetic Resonance Spectrosocpy Ed JW Feeney and LH Sutcliff Pergamon Press London (1969) 4 91 (review)FA Cotton Accounts Chem Res (1968) 1 251 (review)

(Examples of scrambling on carbon)K Moedritzer and JR Van Wazer J Org Chem (1965) 30 3920 (polyoxymethylenes)Ibid (1965) 30 3925 (acetals and orthoformates) JT Bursey MM Bursey and DGI Kingston Chem Rev (1973) 73 191 (intramolecular hydrogen transfer on carbon during mass spectrometery)

Added LaterFollowing my postgraduate research (which had been funded by an Albright amp Wilson Mfg UK Studentship and supervised by DS Payne at the University of Glasgow Scotland UK (earning PhD in 1962 for a thesis lsquoA Study of Phosphitesrsquo [cf D Grant et al J Inorg Nucl Chem 1964 26 1985 and ibid 26 2103) and a study of the use of Ce(IV) for oxidative analytical chemistry [Anal Chim Acta 1961 25 422 ]) I had the honor to work as a Postdoctoral Fellow with John R Van Wazer in his (Monsanto Co St Louis) research group (which conducted fundamental researches into the phenomenon of stochastic structural reorganization this processes which had been found to determine the chemical constitution of condensed phosphates (and further seemed to offer insight into the in biological use of condensed phosphates for energy transfer and as a basic determinant of the structure and activity of nucleic acids) also seemed to allow for a fuller understanding of the thermal stability of numerous kinds of substances (including inorganic organometallic and organic polymers) I later contributed to ISR UK research activities (which ceased in 1975) [cf eg EW Duck et al Eur Polymer J 1974 10 77 ibid 481 ibid 1979 15 625) and ldquoThe Pertinence Of The Scrambling Behaviour of Ligands on Transition-Metal Centres to Ziegler-Natta Catalyst Activitiesrdquo (J Polymer Sci Polymer Lett 1975 13 1 ) which suggested that the polymerization of olefins (as well as the related process of olefin metathesis) occurred by a process akin to Van Wazer structural reorganization at the catalytic center monomer adducts]

DG Note 27412
Van Wazer Structural Reorganization

The Van Wazer method of characterization of chemical systems is useful for the elucidation of the products of synthetic organometallic chemistry where conventional lsquoorganic chemical logicrsquo fails to properly identify the substances formed in any attempted stepwise synthesis of an inorganic molecular structure or a mixed inorganic-organic element (eg B P As Si etc) - containing derivative An example of former situation arose is an attempt to synthesize an ldquoisotetraphosphaterdquo structure While a composition which appeared to contain this structure as suggested by some physical measurements etc seemed to have been produced a later re-evaluation by NMR showed that this structure if formed initially had completely rearranged to produce a reproducible mixture the composition of which could be exactly predicted using the scrambling equilibrium hypothesis suggested by Van Wazer (3) Such rationalizations were similarly useful for arriving at the correct chemical constitution of a product arising from attempts to prepare octamethyltetraminopyrophosphate (((CH3)2N)2P(O))2O) (OMPA) (cf 3a) (the reaction product however showed the NMR spectrum of a completely scrambled mixture of the same stoichiometry A similarly completely scrambled mixture also apparently arose from attempts to prepared specific polysilicate esters eg RO-(Si(OR)2-(O-Si(OR)2)n-O-Si(OR)2-OR (where R is an organic group)