Calorimetric studies of the heats of protonation of the metal in cis-M(CO)2(bidentate phosphine)2 complexes of chromium, molybdenum, and tungsten

John R. Sowa, Jeffrey B. Bonanno, Valerio Zanotti, Robert J. Angelici

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Abstract

Titration calorimetry has been used to determine the heats of protonation (ΔHHM) of cis-M(CO)2(L 'down curve sign' L)2 complexes (M = Cr, Mo, W; L 'down curve sign' L = dppm, dppe, dppp, arphos, dmpe) with CF3SO3H in 1,2-dichloroethane solvent at 25.0°C. Spectroscopic studies show that protonation occurs at the metal center to form [M(H)(CO)2(L 'down curve sign' L)2]CF3SO3 complexes with trans CO groups. For the M(CO)2[Ph2P(CH2)nPh 2]2 complexes, ΔHHM becomes less exothermic as the chelate size increases from n = 1 (-29.7 kcal mol-1) to n = 3 (-19.0 kcal mol-1) for Mo and from n = 1 (-31.5 kcal mol-1) to n = 2 (-25.1 kcal mol-1) for W. The higher basicities of complexes with small chelates are ascribed to distortions imposed on the M(CO)2(L 'down curve sign' L)2 complexes by the chelate ligand and to reduced steric hindrance in the protonated product. Substituting the dppe chelates in Mo(CO)2(dppe)2 (ΔHHM = -27.4 kcal mol-1) with dmpe increases metal basicity (ΔHHM = -38.7 kcal mol-1), and with the arphos ligand metal basicity is decreased (ΔHHM = -23.8 kcal mol-1). In descending group 6, the basicities (ΔHHM) of the M(CO)2(dppm)2 complexes increase in the order Cr (-25.5 kcal mol-1) ≪ Mo (-29.7 kcal mol-1) < W (-31.5 kcal mol-1), but for the M(CO)2(dppe)2 complexes metal basicity decreases in the order Mo (-27.4 kcal mol-1) > W (-25.1 kcal mol-1). The group 8 complex, (η5-C5Me5)2Os (ΔHHM = -26.6 kcal mol-1), is substantially more basic than (η5-C5Me5)2Ru (ΔHHM = -19.0 kcal mol-1). The heats of protonation (ΔHHN) of a series of organonitrogen bases have also been determined.

Original languageEnglish (US)
Pages (from-to)1370-1375
Number of pages6
JournalInorganic Chemistry
Volume31
Issue number8
StatePublished - 1992
Externally publishedYes

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phosphine
Tungsten
Molybdenum
Protonation
Chromium
Carbon Monoxide
chelates
phosphines
molybdenum
chromium
tungsten
Metals
heat
Alkalinity
curves
metals
ligands
titration
heat measurement
Ligands

ASJC Scopus subject areas

  • Inorganic Chemistry

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Calorimetric studies of the heats of protonation of the metal in cis-M(CO)2(bidentate phosphine)2 complexes of chromium, molybdenum, and tungsten. / Sowa, John R.; Bonanno, Jeffrey B.; Zanotti, Valerio; Angelici, Robert J.

In: Inorganic Chemistry, Vol. 31, No. 8, 1992, p. 1370-1375.

Research output: Contribution to journalArticle

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title = "Calorimetric studies of the heats of protonation of the metal in cis-M(CO)2(bidentate phosphine)2 complexes of chromium, molybdenum, and tungsten",
abstract = "Titration calorimetry has been used to determine the heats of protonation (ΔHHM) of cis-M(CO)2(L 'down curve sign' L)2 complexes (M = Cr, Mo, W; L 'down curve sign' L = dppm, dppe, dppp, arphos, dmpe) with CF3SO3H in 1,2-dichloroethane solvent at 25.0°C. Spectroscopic studies show that protonation occurs at the metal center to form [M(H)(CO)2(L 'down curve sign' L)2]CF3SO3 complexes with trans CO groups. For the M(CO)2[Ph2P(CH2)nPh 2]2 complexes, ΔHHM becomes less exothermic as the chelate size increases from n = 1 (-29.7 kcal mol-1) to n = 3 (-19.0 kcal mol-1) for Mo and from n = 1 (-31.5 kcal mol-1) to n = 2 (-25.1 kcal mol-1) for W. The higher basicities of complexes with small chelates are ascribed to distortions imposed on the M(CO)2(L 'down curve sign' L)2 complexes by the chelate ligand and to reduced steric hindrance in the protonated product. Substituting the dppe chelates in Mo(CO)2(dppe)2 (ΔHHM = -27.4 kcal mol-1) with dmpe increases metal basicity (ΔHHM = -38.7 kcal mol-1), and with the arphos ligand metal basicity is decreased (ΔHHM = -23.8 kcal mol-1). In descending group 6, the basicities (ΔHHM) of the M(CO)2(dppm)2 complexes increase in the order Cr (-25.5 kcal mol-1) ≪ Mo (-29.7 kcal mol-1) < W (-31.5 kcal mol-1), but for the M(CO)2(dppe)2 complexes metal basicity decreases in the order Mo (-27.4 kcal mol-1) > W (-25.1 kcal mol-1). The group 8 complex, (η5-C5Me5)2Os (ΔHHM = -26.6 kcal mol-1), is substantially more basic than (η5-C5Me5)2Ru (ΔHHM = -19.0 kcal mol-1). The heats of protonation (ΔHHN) of a series of organonitrogen bases have also been determined.",
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T1 - Calorimetric studies of the heats of protonation of the metal in cis-M(CO)2(bidentate phosphine)2 complexes of chromium, molybdenum, and tungsten

AU - Sowa, John R.

AU - Bonanno, Jeffrey B.

AU - Zanotti, Valerio

AU - Angelici, Robert J.

PY - 1992

Y1 - 1992

N2 - Titration calorimetry has been used to determine the heats of protonation (ΔHHM) of cis-M(CO)2(L 'down curve sign' L)2 complexes (M = Cr, Mo, W; L 'down curve sign' L = dppm, dppe, dppp, arphos, dmpe) with CF3SO3H in 1,2-dichloroethane solvent at 25.0°C. Spectroscopic studies show that protonation occurs at the metal center to form [M(H)(CO)2(L 'down curve sign' L)2]CF3SO3 complexes with trans CO groups. For the M(CO)2[Ph2P(CH2)nPh 2]2 complexes, ΔHHM becomes less exothermic as the chelate size increases from n = 1 (-29.7 kcal mol-1) to n = 3 (-19.0 kcal mol-1) for Mo and from n = 1 (-31.5 kcal mol-1) to n = 2 (-25.1 kcal mol-1) for W. The higher basicities of complexes with small chelates are ascribed to distortions imposed on the M(CO)2(L 'down curve sign' L)2 complexes by the chelate ligand and to reduced steric hindrance in the protonated product. Substituting the dppe chelates in Mo(CO)2(dppe)2 (ΔHHM = -27.4 kcal mol-1) with dmpe increases metal basicity (ΔHHM = -38.7 kcal mol-1), and with the arphos ligand metal basicity is decreased (ΔHHM = -23.8 kcal mol-1). In descending group 6, the basicities (ΔHHM) of the M(CO)2(dppm)2 complexes increase in the order Cr (-25.5 kcal mol-1) ≪ Mo (-29.7 kcal mol-1) < W (-31.5 kcal mol-1), but for the M(CO)2(dppe)2 complexes metal basicity decreases in the order Mo (-27.4 kcal mol-1) > W (-25.1 kcal mol-1). The group 8 complex, (η5-C5Me5)2Os (ΔHHM = -26.6 kcal mol-1), is substantially more basic than (η5-C5Me5)2Ru (ΔHHM = -19.0 kcal mol-1). The heats of protonation (ΔHHN) of a series of organonitrogen bases have also been determined.

AB - Titration calorimetry has been used to determine the heats of protonation (ΔHHM) of cis-M(CO)2(L 'down curve sign' L)2 complexes (M = Cr, Mo, W; L 'down curve sign' L = dppm, dppe, dppp, arphos, dmpe) with CF3SO3H in 1,2-dichloroethane solvent at 25.0°C. Spectroscopic studies show that protonation occurs at the metal center to form [M(H)(CO)2(L 'down curve sign' L)2]CF3SO3 complexes with trans CO groups. For the M(CO)2[Ph2P(CH2)nPh 2]2 complexes, ΔHHM becomes less exothermic as the chelate size increases from n = 1 (-29.7 kcal mol-1) to n = 3 (-19.0 kcal mol-1) for Mo and from n = 1 (-31.5 kcal mol-1) to n = 2 (-25.1 kcal mol-1) for W. The higher basicities of complexes with small chelates are ascribed to distortions imposed on the M(CO)2(L 'down curve sign' L)2 complexes by the chelate ligand and to reduced steric hindrance in the protonated product. Substituting the dppe chelates in Mo(CO)2(dppe)2 (ΔHHM = -27.4 kcal mol-1) with dmpe increases metal basicity (ΔHHM = -38.7 kcal mol-1), and with the arphos ligand metal basicity is decreased (ΔHHM = -23.8 kcal mol-1). In descending group 6, the basicities (ΔHHM) of the M(CO)2(dppm)2 complexes increase in the order Cr (-25.5 kcal mol-1) ≪ Mo (-29.7 kcal mol-1) < W (-31.5 kcal mol-1), but for the M(CO)2(dppe)2 complexes metal basicity decreases in the order Mo (-27.4 kcal mol-1) > W (-25.1 kcal mol-1). The group 8 complex, (η5-C5Me5)2Os (ΔHHM = -26.6 kcal mol-1), is substantially more basic than (η5-C5Me5)2Ru (ΔHHM = -19.0 kcal mol-1). The heats of protonation (ΔHHN) of a series of organonitrogen bases have also been determined.

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