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Terry Tao
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From the results of

Brown, Arlen; Pearcy, Carl, Structure of commutators of operators, Ann. Math. (2) 82, 112-127 (1965). ZBL0131.12302.

an element of $B(H)$ is a commutator $xy-yx$ if and only if it is not of the form $\lambda I + C$ for some non-zero scalar $\lambda$ and compact $C$. So one can for instance take $A$ to be the unital commutativeyour algebra generated bywould have to contain an arbitrary compactelement of the form $\lambda I + C$ but not $C$ to answer your question in(unless $C=0$), and so cannot contain the positivescalars unless it consisted solely of the scalars, which are indeed not commutators by the classical results of Wintner and Wielandt.

From the results of

Brown, Arlen; Pearcy, Carl, Structure of commutators of operators, Ann. Math. (2) 82, 112-127 (1965). ZBL0131.12302.

an element of $B(H)$ is a commutator $xy-yx$ if and only if it is not of the form $\lambda I + C$ for some scalar $\lambda$ and compact $C$. So one can for instance take $A$ to be the unital commutative algebra generated by an arbitrary compact $C$ to answer your question in the positive.

From the results of

Brown, Arlen; Pearcy, Carl, Structure of commutators of operators, Ann. Math. (2) 82, 112-127 (1965). ZBL0131.12302.

an element of $B(H)$ is a commutator $xy-yx$ if and only if it is not of the form $\lambda I + C$ for some non-zero scalar $\lambda$ and compact $C$. So your algebra would have to contain an element of the form $\lambda I + C$ but not $C$ (unless $C=0$), and so cannot contain the scalars unless it consisted solely of the scalars, which are indeed not commutators by the classical results of Wintner and Wielandt.

Source Link
Terry Tao
  • 114.2k
  • 33
  • 462
  • 539

From the results of

Brown, Arlen; Pearcy, Carl, Structure of commutators of operators, Ann. Math. (2) 82, 112-127 (1965). ZBL0131.12302.

an element of $B(H)$ is a commutator $xy-yx$ if and only if it is not of the form $\lambda I + C$ for some scalar $\lambda$ and compact $C$. So one can for instance take $A$ to be the unital commutative algebra generated by an arbitrary compact $C$ to answer your question in the positive.