INORGANIC CHEMISTRY CHEM 462
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Date Created: 10/21/15
Selections from Chapter 14 Reactions of Coordination Compounds CHEM 462 December 6th T Hughbanks Ligand Substitution Reactions 0 Reminders kinaic terms Labile Vs Inert thermodynamicterms Stable Vs Urstable o eg athennodynamically favored slow reaction CoN39H353 6 H30 Co9053 6 N39Hf K 10ZS o Ligand substitution the two extremes N j MX gt LSNI X slow dissociaive I MY gt LSMY fast 5N2 I MXY gt I MXY slow associative LSMXY gt LSMY X fat Rate Laws 0 Ligand substitution the two rate laws 5N1 15MX ALSM X slow dissociative L5MY gt L MY fat ratekL5MX 5N2 LSMX Y gt LSMXY slow associative LSMXY gt LSMY X fat as k LSMXHY Complications o Conjugate base formation ifthe complex has acidic protons e g basic catalysis CoN39H35ClZ OH CoNH3NHZc1 HZO fast CoNH3Nnc1 gt CoN39H34N39HiZ Cl slow CdNH3tNHzl Yi39 gt CdN39H AN39HDYl fat CdN39H3N39H Y HZO C0N39H35YZ OH fast es it make sense that the 2nd step is slow Q2 Why does the deptotonate ex more lose Cl faster thanthe original oomplex rate x complex OH Solvent Intervention esp H20 0 Suppose solvent H20 intervenes in rate det step LnMXHiO gt LnMHiO X slow LnMHiO gt LnMY m0 fat Either step could be asociaivegr dissociaive but either bsd ratex LHMX ie me not dependent on Y amp HZO is essentially const 0 example square planar complexes of Pt 1 PIL3X obsd rate k Pth Y 1 PIL3gtlt H20 1 fHQO fast PtLgXHY k2 7 both pathways Y P1L3X are associative More Complications IonePairs outeresphere complex formation L5MX39 Ym39 L5lJXYquotquotquot ionepair complex 0 bonds made or broken 2nd step L5lJXYltquot quot0 a L5MY X slow obs rate x LSMXY 7 this is the expected rate law whether or not the mechanism is associative in the sense that a L5MXY complex forms Mechanistic Clues oActiwtion parameters AH AS AV I How are each ofthese measured oFor dissociative reactions we expect that all of these will be gt 0 Water Exchange Rates Water Exchange Rates oFor alkali and alkaline earth dissociative chanism seems to hold throughout rates increase with ionic size M MVOHZ bonds weaken with increming ion size MVOHZ bonds break intmrsition state lt La M ions Sc3lt Y Al lt Ga lt In Trends for TMs Wt M gt Co gt Cr Cu gt Fe3 gt an Zn Does this LFSE trend correlate with exchange rates AV1gt 0 for W C02 Ni2 but AV1lt 0 for W Mn2 Co Rh Ir Cr all quite inert 7 all have high LFSE39S Associative vs Dissociative AV1 measurements indicate mechanisms may differ in seemingly similar reactions CoNH35HZO3 Cl gt CoNH35C12 H20 Av1 14 08 cm3 molquot RhNH35HZO3 Cl gt RhNH35C12 H20 Av1 30 t 07 cm3 molquot CrltNH3gt5H20gt3 Cl a CrNH35C12 H20 Av1 749 i 08 cm3 molquot Anation Reactions 0 Replacement of water by incoming anion ML5HZOZ X gt Ml x H20 0 General Observations ae epends on complex but dependence on incoming ligand if any involves only concentraionnot on identity of anion 2 rates for anaion compaiable to water exchange anations for anaion of aquo ions MHZO quot x7 MHZO X0 no onlenspnere complex MH10 Xgtl 1 v r gt MHZO5X 1 HZO slow me x 1 4H 05quotX Anatiori of anionic complexes no ionepairing egi C0CN5H20lZ39 C0CN5lZ39 H2 In some cases one can distinguish between different incoming anions39 depends on x cqcmsizn x COCN512 COCNSHZO239 axwa ix H20 Substitution Rxns on Sq Planar Complexes 0 Stereochemistry is preserved Mechanism Replacement of C with X i i Ei F39t C gt B PI t C LJ x x U Ei F39 We x c D F mi Ei F39t X 4 n PL H 9 Q How can traces of quot quot Trans Effect Ligand exchange reactions can be directed by the labilizing ability of ligands in trans positio L X L Y L X PI gt P1 or PI iQ Y Y product depends labilizing ability Trans effect series 000N102H4 gt PR3 H gt CH gt 05H N02 I SCN gt Br CI gt py NH3 OH H2O Stereochemical Control Examples C 0 TI7 C NH3 V V P 0 l 0 NH3 0 NH3 cis 2 HN H c E 0 NH 3v 1 V 1 V 3 H3N NH3 NH3 NH3 H3N Cl trans Problems 0 Give synthetic routes to cis7 and trans PtClZNH3NOZ 0 Consider a reaction of the type transiPtLZClZ Y gt z rcmsiH tLZClYTr Cl what complications might arise if the intermediate in this reaction is has a fairly long lifetime 0 The reaction below can be carried out in liquid ammonia but is very slow unless a small amount of KNHZ is added Why CrNH35ClZ NH3 gt CrNH353 Cl